Boulder Run

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Boulder Run is a free online cave digging game for one player, and the thing that makes it a puzzle rather than a chase is that nothing in it wants to hurt you. Every boulder is held up by the dirt beneath it, and you are the one removing the dirt. Dig under a rock while standing under it and it lands on your head, and that is entirely your own doing. A rock that lands on another rock rolls off the side if the side is clear, so a cell you dug two moves ago becomes an avalanche now, somewhere you were not looking. The only force you have is a shove: a boulder with clear space behind it can be pushed sideways, one cell at a time, and that is it — you cannot lift one, you cannot dig it out, and you cannot get it back once it has rolled. Each cave asks for a number of gems before the way out opens, so you cannot simply walk to the exit, and gems fall exactly like rocks, which means a gem sitting over a hole you just dug is a gem that is about to be somewhere else. A gem grabbed while a rock is already falling somewhere is worth extra, which is the game quietly paying you for nerve. Four caves, three lives, more rock in each, a clock per cave, and a fixed-step simulation with a seeded generator, so Replay digs exactly the same cave.

How to play Boulder Run

1. Press Play. You start in a small pocket at the top left of the cave.
2. Arrow keys or WASD dig. Walking into dirt removes it; walking into open space just moves you.
3. Collect the number of gems the cave asks for — the counter is at the top. Only then does the way out, at the bottom right, open.
4. A boulder with nothing under it falls. Nothing else in the cave moves on its own, so every fall is a consequence of something you dug.
5. A falling boulder that lands on you costs a life. One that is already resting on something is harmless.
6. A boulder that lands on another boulder rolls off to the side if that side is clear — which is how one dug cell becomes an avalanche two moves later.
7. You can push a boulder sideways into clear space. You cannot push one up, down, or into anything.
8. Gems fall exactly like boulders, so one sitting over a hole you just dug will not be there when you get back.
9. A gem taken while something is already falling somewhere is worth extra.
10. Each cave has a clock. Running it out costs a life, and losing a life digs the cave again from scratch.
11. Four caves, each with more rock than the last, and three lives for the whole run.

Tips

• Look up before you dig. The single most common death here is digging straight down into a cell with a boulder directly above it — a bot that never looked up died three times out of three in every run.
• Dig sideways along a row rather than down a column. A horizontal tunnel puts you beside falling rock instead of under it.
• Under the top wall is the safest ground in the cave: nothing can fall on you there.
• After you dig out a support, move before it lands. A rock takes a moment to start falling, and that moment is the whole margin.
• Take the gems at the edge of a rock field first. The ones in the middle get buried by the collapse the first dig sets off.
• A push is one cell at a time, so plan pushes with the space behind the rock in mind — there is no undo, and a rock that rolls somewhere awkward stays there.
• Count the quota. You rarely need every gem in the cave, and the last few are usually the ones under the worst rock.
• When the clock gets low, head for the exit with the quota met rather than greedily topping up. The bonus for time left is real but the cave takes lives, not points.

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