This puzzle was constructed in collaboration with Wessel Strijkstra by passing the puzzle back and forth, adding one clue at a time.

The CTC Discord server hosts a “monthly puzzle prompt” that I’ve been meaning to make something for since joining the server over two years ago. However, for one reason or another it never worked out. This month’s prompt was for two authors to write a puzzle together by taking turns adding clues, so I asked Wessel if he’d be interested. We quickly agreed that we wanted to use a genre or variant with two clue types of roughly similar strength, so each one of us could pick one type. After some brainstorming, Wessel suggested Cave (LITSO) and we went with that. I placed the number clues and he placed the letter clues.

I don’t think we ever talked about it, but we just both decided not to go for any visual theme and instead focus entirely on an interesting solve path. I think that worked out pretty well. Due to the process, we ended up with a puzzle where every single clue does quite a lot of work and the solve path alternates between both parts of the ruleset in a satisfying way.

For answer check, draw lines along the shaded cells to indicate the tetrominoes.

Solve it online:

**Rules:** Shade some cells so that the shaded cells are all connected orthogonally by other shaded cells to the edge of the grid, and the remaining unshaded cells form one orthogonally connected area.

The shaded cells must also be able to be divided into tetrominoes such that no two tetrominoes of the same shape share an edge, counting rotations and reflections as the same.

Number clues cannot be shaded, and represent the total number of unshaded cells that can be seen in a straight line vertically or horizontally, including itself.

Letter clues must be shaded, and must belong to a tetromino corresponding to that letter.