Grandpa's Lighthouse.

Tap or click anything in the room to look closer; Grandpa's letter on the table is the place to start. Each lock is a small puzzle. Solving it opens something, and what you find goes into your pocket.

Some locks need what another lock gave you, so they open in one order. When the last one opens, you climb the stairs and light the lamp, so Grandma's boat finds its way into the harbour.

The sea chest has a picture grid: the numbers by each row and column tell how many cells in a row are filled. The signal line takes five flags in the order of Grandpa's rhyme. The logbook hides its word by moving letters along the alphabet. The cabinet has three dials, and something in the room tells you what to set.

The pebble board wants one pebble in every row, every column and every coloured patch, with no two pebbles touching, not even at a corner. The stair door has a sum plate: every row and column adds up to its number, and no digit appears twice in a row or a column.

Every lock has exactly one answer, and none of them needs a guess.

Hint answers in two steps, in the bar under the room. The first press says where to look and why. The second press does exactly one step for you: it fills a row, sets a wheel, places a pebble or writes a digit. When you are in the room rather than a puzzle, the second press lights up the thing to open next.

If a mark on a puzzle is wrong, the first hint says so and the second clears it. Hints are free and have no limit. One hint counts once, whether you stop after the first press or take the second too. At the end, a lock is marked as helped only when a hint helped with its puzzle; a hint that just shows you where to go counts in your total, not against a lock.

Keyboard: Tab moves between the things in the room, Enter or Space opens one, Esc goes back to the room.

In the picture grid and on the pebble board, arrows move and Space cycles a cell. On the letter wheels and the dials, up and down arrows turn, left and right arrows move, and you can simply type the letter or digit. On the sum plate, arrows move and digits write. On the signal line, Enter picks up a flag, arrows carry it and Enter puts it down.

The picture grid, the pebble board and the sum plate have Undo and Redo, as in our daily puzzles: U or Ctrl+Z undoes, R or Ctrl+Y redoes, and Clear can be undone too.

Everything is saved in this browser as you go: open locks, your pocket, half finished puzzles, time and hints. Close the page and come back later.

The clock runs only while you play. It stops when you leave the tab or do nothing for a minute, and Pause stops it too. Settings has Start again.