Ignore the open doors, it’s the locked gate you want to go through.

The coloured tiles on the floor on the other side of the room are a puzzle that unlocks the gate. The puzzle is operated by the sound of a crossbow being fired. Lucky for you, you’re carrying one of those!

Whenever you shoot, the four tiles around the white marker will rotate their positions. You need to rearrange the tiles so that they line up in rows matching the three colours on the wall (green on the left, pink in the middle, yellow on the right). This isn’t too difficult. Line up the three green tiles on the left first (the green mark on the wall will go dark) then shuffle the pink and yellow tiles into place.

When the gate is open, go through the door at the bottom of the picture.