Here are all positions of the fragment. Set the sliders as shown below to connect the pairs. Rotate the wheel with the crowns anti-clockwise and extract the key. If you’re done with all the other puzzles, you can take out the inner box. Otherwise check the steps 1-4 above.

When you see through the keyhole, you may distinguish the shapes of runes inside. They have the same positions as the spiked balls.

The slider on the box can move, but you should unlock it first. Pay attention to the note symbol which unlocks the slider. If your container looks like this, also pay attention to the lines.

Note each spiked ball is connected to a gear via chain.

The same note symbol can be found on the image of the trumpet.

Set the runes on the gears as shown below. Then take out the the key.

Note the container intentionally represents a wind instrument. What can you do with such instruments?

Look at the space underneath the towers puzzle (if you haven’t solved the towers yet, see Puzzle 2). There are blocked parts in the middle, you need to release them.

To unlock the slider, you should blow into one of two holes. Hold the box vertically in front of your lips as if it were a trumpet. Blow sharply into the right hole. You don’t have to touch it with your lips, a small distance is enough. While blowing, hold the sliding element upwards.

Pay attention to the arrows.

The parts of the sword should be somehow put together

To release the parts, you have to push the sliders in opposite directions simultaneously. Then turn over the box – the unlocked parts will fall down.