Party Crasher Trophy in Apotheon

First, go to the Agora. The first door to the right of the Market door will be a locked door that leads to a house. Enter it (pick the lock) and get the Symposium of the Sun Seal. Then go to Apollo's main area – you will see a locked door right in the middle of it, on the main level. Open it with the Symposium of the Sun Seal, enter, and the trophy unlocks right away.