Jabba's Palace is Jabba the Hutt's personal palace on Tatooine. Jabba, being sort of space mobster, leads all his illegal activities from his palace. He has a giant front door where a spider like eye scans visitors. He hangs out with a posse of bounty hunters which he sends out to do his evil biddings. He also has the Ranckor, a giant monster that eats prisoners and guards alike, hidden deep down in the palace's dungeons.
The Palace is mostly seen in Star Wars Episode VI. It's the setting for the entire first act. Luke Skywalker must go there to free his friends after Leia fails in rescuing Han Solo. This scene is depicted in the Lego Star Wars games.
Jabba's Palace can be seen in Star Wars IV: A New Hope.