For many years The grand structure of the palace belonged to Jabba's father, upon his arrest Jabba set about re-designing the palace with his architect Deren Flet (who was sadly killed by Jabba after an misunderstanding about the lower dungeons of the palace (or lack of them!)
The top floor of the Palace is Jabba's throne and entertaiment room, the lower regions are reserved for Jabba'a enemies who are subject to pain, torture and slow deaths, they also house the great beast (Jabba's main source of torture) the Rancor.
A network of security scanners detect visitors from 10 km away and the main gate is guarded by a one eyed droid who makes sure un-welcome visitors are kept well away from the palace.