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Wall off the rock so one connected cave remains, and every number sees exactly that many cave squares along its row and column.
Every square on the seven by seven board is either cave or rock. Tap a square once to turn it into rock, twice to mark it as cave for your own notes, and three times to clear it again. Only the rock you place is checked, so the marks are purely an aid.
The cave has to end up as one connected piece, joined edge to edge. All the rock has to reach the outside of the board through other rock, so you can never seal a pocket of rock inside the cave.
A numbered square is always part of the cave, and its number counts how many cave squares it can see: itself, plus everything running up, down, left and right until rock blocks the line of sight.
Every board is checked twice before it reaches you. It has exactly one solution, and that solution can be reached by deduction alone, so there is never a point where you have to guess and back up. Your time is your score, so lower is better.
Start with the biggest and the smallest numbers, because they are the ones that say the most. A one is the strongest clue on the board: it sees only itself, so all four of its neighbours are rock. A number as large as ten or twelve is nearly as good, because it has to reach a long way in two directions at once, which forces a whole row or column open.
The cheapest deduction is a bound, not a guess. For each number, add up how far it could possibly see if every unknown square around it were cave. If that maximum equals the number, every one of those squares is cave. Do the same from the other side: if the squares you already know are cave already add up to the number, then the next unknown square in each of the four directions must be rock. Most of a board falls out of those two checks alone.
Connectivity does as much work as arithmetic here, and beginners skip it. Before placing a rock, ask whether it would cut the cave in two, or whether it would trap a rock square inside with no path to the edge. Squares in the corners and along the sides are where this bites first, because they have fewer ways out.
When you get stuck, try a square both ways in your head rather than staring harder. Suppose it is rock: if that splits the cave or breaks a count, it must be cave. That single-square test is exactly what the generator uses to guarantee every board can be solved without guessing, so if you are stuck, a test like that always exists somewhere.