This can only be obtained during the Twins playthrough.
While in the twins house there are technically 2 ways to obtain this trophy.
Way 1
When getting the chamberpot from your parent's bedroom, jump on the bed three times.
Way 2
After obtaining the skeleton key, go to the right inside to the living room where there are two book shelves. Press square three times while standing in front of the right hand shelf. There is also a cave painting behind this shelf.