Find out where you have seen the Mansion before.
In the Mushroom Forest, walk all the way to the left in order to find the passage that leads to a beach where the fisherman from the I Can't Swim... event can be found. Talk to him and he will offer Tomba a ride.
Upon arriving, head right to trigger a short sequence where the camera scrolls upwards to reveal a mansion. The event is now activated.
Go through the doorway on the right and walk through two rooms to go outside of the mansion and reveal that the mansion was in fact the same mansion found in the Village of All Beginnings. The event is cleared.