She has owned the house for decades. 
The townhouse is five stories tall; has a gargoyle-shaped door knocker; a two-car garage; a fountain; and is surrounded by a brick wall with two gates monitored by security cameras. The front door is also monitored by security cameras. There is also a satellite dish on the roof.
Demona summoned Puck through Titania's Mirror in her fifth floor study. There is no balcony to be seen, but there are three large windows on the top floor she can keep shuttered, but she opened one to experience her first sunrise and it can be assumed this is how she comes and goes at night.
In the Radio Play, Demona brought Eddie Brock, John Jameson, Dominic Dracon, and Cletus Kasady to the townhouse after breaking them out of Ravencroft. After her thieves delivered the Spear of Destiny to her, she used it to restore Eddie to being Venom, Jameson to being Colonel Jupiter, and here she used Cletus Kasady to create Carnage.