There are 4 hidden chests that can be found in the Krypt. Each chest will give you a bonus of 5000 Koins. It takes just a few minutes.
Each area has one secret chest. You have to examine a certain object to make it appear. Stand in front it for a couple seconds until the chest pops out. The fact that you need to look at it for so long makes those things very easy to miss. Actually, the Krypt is not so roomy and this will make the treasures easy to find when knowing their location. Check out your map and compare it with the map, shown in the video to reach the places fast and easy.