Harley Quinn Wiki

Poison Ivy
My question is where did he find the contractor to do all this? You know what I'm saying?
Doctor Trap
Please, evil construction is a blooming business in New New Gotham.
— "Catwoman"

The Gotham Natural History Museum is a large museum located in Gotham City.

When the city fell after the events of "Devil's Snare", Doctor Trap looted a bunch of villains' lairs and collected various object which he all displayed in the museum. To keep people from stealing his loot, he filled the museum with dangerous traps. In "Catwoman" after finding out he had Firefly's flamethrower which they needed to break into Mister Freeze's lair, Harley Quinn and Poison Ivy decided to break into the museum. With the help of Catwoman they managed to avoid the traps and get out with the flamethrower.