diff --git a/.aoc-cache/16.txt b/.aoc-cache/16.txt
new file mode 100644
index 0000000..19418dd
--- /dev/null
+++ b/.aoc-cache/16.txt
@@ -0,0 +1,52 @@
+Valve JZ has flow rate=0; tunnels lead to valves IR, LY
+Valve KD has flow rate=0; tunnels lead to valves NJ, ZS
+Valve VW has flow rate=0; tunnels lead to valves IT, VH
+Valve HS has flow rate=0; tunnels lead to valves OC, PN
+Valve EU has flow rate=19; tunnel leads to valve GQ
+Valve XF has flow rate=0; tunnels lead to valves WL, QD
+Valve DD has flow rate=8; tunnels lead to valves GQ, YY, JV, SK
+Valve TA has flow rate=0; tunnels lead to valves NJ, VJ
+Valve IR has flow rate=9; tunnels lead to valves JZ, WI, VJ, GC, WG
+Valve SS has flow rate=17; tunnels lead to valves SI, IZ, RK, WI
+Valve SG has flow rate=0; tunnels lead to valves NV, NJ
+Valve IT has flow rate=0; tunnels lead to valves LL, VW
+Valve CP has flow rate=24; tunnels lead to valves HN, ZK, EJ
+Valve SK has flow rate=0; tunnels lead to valves LL, DD
+Valve IS has flow rate=0; tunnels lead to valves AA, LL
+Valve HN has flow rate=0; tunnels lead to valves FF, CP
+Valve VH has flow rate=10; tunnels lead to valves QO, VW, RV, PN
+Valve JV has flow rate=0; tunnels lead to valves DD, RK
+Valve ZS has flow rate=0; tunnels lead to valves KD, LL
+Valve UC has flow rate=25; tunnels lead to valves JD, IV
+Valve WI has flow rate=0; tunnels lead to valves SS, IR
+Valve UR has flow rate=0; tunnels lead to valves QD, LY
+Valve GC has flow rate=0; tunnels lead to valves AA, IR
+Valve YY has flow rate=0; tunnels lead to valves DD, AA
+Valve IV has flow rate=0; tunnels lead to valves ZK, UC
+Valve BM has flow rate=0; tunnels lead to valves SA, WL
+Valve JD has flow rate=0; tunnels lead to valves IZ, UC
+Valve WL has flow rate=12; tunnels lead to valves EF, BM, EJ, XF
+Valve AA has flow rate=0; tunnels lead to valves NV, YY, GC, IS, QO
+Valve WG has flow rate=0; tunnels lead to valves LL, IR
+Valve GQ has flow rate=0; tunnels lead to valves EU, DD
+Valve SI has flow rate=0; tunnels lead to valves SS, NJ
+Valve KH has flow rate=13; tunnels lead to valves SA, ON
+Valve PC has flow rate=22; tunnel leads to valve ON
+Valve QD has flow rate=14; tunnels lead to valves XF, UR
+Valve IZ has flow rate=0; tunnels lead to valves SS, JD
+Valve QO has flow rate=0; tunnels lead to valves AA, VH
+Valve SA has flow rate=0; tunnels lead to valves BM, KH
+Valve NV has flow rate=0; tunnels lead to valves AA, SG
+Valve ZK has flow rate=0; tunnels lead to valves CP, IV
+Valve ON has flow rate=0; tunnels lead to valves PC, KH
+Valve PN has flow rate=0; tunnels lead to valves HS, VH
+Valve RV has flow rate=0; tunnels lead to valves NJ, VH
+Valve RK has flow rate=0; tunnels lead to valves SS, JV
+Valve OC has flow rate=18; tunnel leads to valve HS
+Valve EF has flow rate=0; tunnels lead to valves LY, WL
+Valve VJ has flow rate=0; tunnels lead to valves TA, IR
+Valve LL has flow rate=5; tunnels lead to valves ZS, IT, SK, IS, WG
+Valve FF has flow rate=0; tunnels lead to valves HN, LY
+Valve LY has flow rate=21; tunnels lead to valves EF, FF, UR, JZ
+Valve EJ has flow rate=0; tunnels lead to valves WL, CP
+Valve NJ has flow rate=6; tunnels lead to valves RV, KD, SG, SI, TA
diff --git a/src/bin/day_16.rs b/src/bin/day_16.rs
new file mode 100644
index 0000000..52d2a15
--- /dev/null
+++ b/src/bin/day_16.rs
@@ -0,0 +1,264 @@
+use std::collections::{HashMap, HashSet};
+
+use aoc_2022::prelude::*;
+
+use lru_cache::LruCache;
+use regex::Regex;
+
+type Input = HashMap<String, Valve>;
+
+#[derive(Debug)]
+struct Valve {
+    flow_rate: usize,
+    tunnels: Vec<String>,
+}
+
+fn parse(s: &str) -> Result<Input> {
+    let re = Regex::new("Valve ([A-Z]{2}) has flow rate=([0-9]+)")?;
+
+    let mut valves = HashMap::new();
+
+    for line in s.lines() {
+        let (a, b) = line.split_once("; ").unwrap();
+        let captures = re.captures(a).unwrap();
+        let name = captures.get(1).unwrap().as_str().to_owned();
+        let flow_rate = captures.get(2).unwrap().as_str().parse()?;
+
+        let tunnels = b
+            .trim_start_matches("tunnel leads to valve")
+            .trim_start_matches("tunnels lead to valves")
+            .trim_start()
+            .split(", ")
+            .map(|s| s.to_owned())
+            .collect();
+
+        valves.insert(name, Valve { flow_rate, tunnels });
+    }
+
+    Ok(valves)
+}
+
+#[aoc(day = 16, parse = parse, test_cases = ["day_16.txt"])]
+fn day_16(input: Input) -> Result<()> {
+    // Part 1
+    let (_path, greatest) = explore(
+        &input,
+        29,
+        "AA",
+        &HashSet::new(),
+        "AA".to_owned(),
+        &mut HashMap::new(),
+    );
+    println!("Part one: {greatest}");
+    // println!("{path}");
+
+    // Part 2
+    let greatest = explore_with_elephant(
+        &input,
+        25,
+        "AA",
+        "AA",
+        &HashSet::new(),
+        &mut LruCache::new(4_000_000),
+    );
+    println!("Part two: {greatest}");
+    Ok(())
+}
+
+#[derive(Clone)]
+enum Action<'a> {
+    Open,
+    MoveTo(&'a str),
+    DoLiterallyNothingForAMinute,
+}
+
+fn sum_flow(input: &Input, open: &HashSet<String>) -> usize {
+    open.iter().map(|n| input[n].flow_rate).sum()
+}
+
+fn encode_open(open: &HashSet<String>) -> String {
+    let mut result = String::new();
+    let mut open_vec = open.iter().collect::<Vec<_>>();
+    open_vec.sort();
+    for n in open_vec {
+        result.push_str(n);
+    }
+    result
+}
+
+fn explore(
+    input: &Input,
+    depth: usize,
+    node: &str,
+    open: &HashSet<String>,
+    path: String,
+    cache: &mut HashMap<(usize, String, String), (String, usize)>,
+) -> (String, usize) {
+    let pressure_this_round = sum_flow(input, &open);
+
+    let cache_key = (depth, node.to_owned(), encode_open(open));
+    if let Some(result) = cache.get(&cache_key) {
+        return (result.0.clone(), pressure_this_round + result.1);
+    }
+
+    if depth == 0 {
+        return (path, pressure_this_round);
+    }
+
+    let current = &input[node];
+    let mut actions = current
+        .tunnels
+        .iter()
+        .map(|tunnel| Action::MoveTo(&*tunnel))
+        .collect::<Vec<_>>();
+
+    actions.push(Action::DoLiterallyNothingForAMinute);
+
+    if current.flow_rate != 0 && !open.contains(node) {
+        actions.insert(0, Action::Open);
+    }
+
+    let result = actions
+        .iter()
+        .map(|action| match action {
+            Action::Open => {
+                let mut open = open.clone();
+                open.insert(node.to_owned());
+                explore(
+                    input,
+                    depth - 1,
+                    node,
+                    &open,
+                    format!("{path}\n*open* ({pressure_this_round})"),
+                    cache,
+                )
+            }
+            Action::MoveTo(n) => explore(
+                input,
+                depth - 1,
+                *n,
+                open,
+                format!("{path}\nmove to {n} ({pressure_this_round})"),
+                cache,
+            ),
+            Action::DoLiterallyNothingForAMinute => explore(
+                input,
+                depth - 1,
+                node,
+                open,
+                format!("{path}\n*wait* ({pressure_this_round})"),
+                cache,
+            ),
+        })
+        .max_by_key(|r| r.1)
+        .unwrap();
+
+    cache.insert(cache_key, result.clone());
+
+    (result.0, result.1 + pressure_this_round)
+}
+
+fn explore_with_elephant(
+    input: &Input,
+    depth: usize,
+    my_node: &str,
+    elephant_node: &str,
+    open: &HashSet<String>,
+    cache: &mut LruCache<(usize, String, String, String), usize>,
+) -> usize {
+    let pressure_this_round = sum_flow(input, &open);
+
+    let cache_key = (
+        depth,
+        my_node.to_owned(),
+        elephant_node.to_owned(),
+        encode_open(open),
+    );
+    if let Some(result) = cache.get_mut(&cache_key) {
+        return pressure_this_round + *result;
+    }
+
+    if depth == 0 {
+        return pressure_this_round;
+    }
+
+    let my_actions = {
+        let current = &input[my_node];
+        let mut my_actions = current
+            .tunnels
+            .iter()
+            .map(|tunnel| Action::MoveTo(&*tunnel))
+            .collect::<Vec<_>>();
+
+        my_actions.push(Action::DoLiterallyNothingForAMinute);
+
+        if current.flow_rate != 0 && !open.contains(my_node) {
+            my_actions.insert(0, Action::Open);
+        }
+
+        my_actions
+    };
+
+    let elephant_actions = {
+        let current = &input[elephant_node];
+        let mut elephant_actions = current
+            .tunnels
+            .iter()
+            .map(|tunnel| Action::MoveTo(&*tunnel))
+            .collect::<Vec<_>>();
+
+        elephant_actions.push(Action::DoLiterallyNothingForAMinute);
+
+        if current.flow_rate != 0 && !open.contains(elephant_node) {
+            elephant_actions.insert(0, Action::Open);
+        }
+
+        elephant_actions
+    };
+
+    let paired_actions = my_actions
+        .into_iter()
+        .flat_map(|action| {
+            elephant_actions
+                .iter()
+                .map(Clone::clone)
+                .map(move |a| (action.clone(), a))
+        })
+        .filter(|(a, b)| match (a, b) {
+            (Action::Open, Action::Open) => false,
+            _ => true,
+        });
+
+    let result = paired_actions
+        .map(|(my_action, elephant_action)| {
+            let (open, my_node) = match my_action {
+                Action::Open => {
+                    let mut open = open.clone();
+                    open.insert(my_node.to_owned());
+                    (open, my_node.to_owned())
+                }
+                Action::MoveTo(node) => (open.clone(), node.to_owned()),
+                Action::DoLiterallyNothingForAMinute => (open.clone(), my_node.to_owned()),
+            };
+
+            let (open, elephant_node) = match elephant_action {
+                Action::Open => {
+                    let mut open = open.clone();
+                    open.insert(elephant_node.to_owned());
+                    (open, elephant_node.to_owned())
+                }
+                Action::MoveTo(node) => (open.clone(), node.to_owned()),
+                Action::DoLiterallyNothingForAMinute => (open.clone(), elephant_node.to_owned()),
+            };
+
+            explore_with_elephant(input, depth - 1, &my_node, &elephant_node, &open, cache)
+        })
+        .max()
+        .unwrap();
+
+    if depth < 10 || depth > 20 {
+        cache.insert(cache_key, result);
+    }
+
+    result + pressure_this_round
+}
diff --git a/test_cases/day_16.txt b/test_cases/day_16.txt
new file mode 100644
index 0000000..85fa5b0
--- /dev/null
+++ b/test_cases/day_16.txt
@@ -0,0 +1,10 @@
+Valve AA has flow rate=0; tunnels lead to valves DD, II, BB
+Valve BB has flow rate=13; tunnels lead to valves CC, AA
+Valve CC has flow rate=2; tunnels lead to valves DD, BB
+Valve DD has flow rate=20; tunnels lead to valves CC, AA, EE
+Valve EE has flow rate=3; tunnels lead to valves FF, DD
+Valve FF has flow rate=0; tunnels lead to valves EE, GG
+Valve GG has flow rate=0; tunnels lead to valves FF, HH
+Valve HH has flow rate=22; tunnel leads to valve GG
+Valve II has flow rate=0; tunnels lead to valves AA, JJ
+Valve JJ has flow rate=21; tunnel leads to valve II
\ No newline at end of file