A's Dollhouse is a fully built underground lair belonging to A. It has exact replicas of The Liars' bedrooms except for Mona's (instead, Mona sleeps in a replica of Ali's bedroom because A wants Mona to believe she is Ali). A installed cameras in every room and is able to stalk the girls while sitting in his lair. There's also a vocal system installed which tells the girls what to do. It was first shown in Welcome to the Dollhouse, the episode when the Liars, except Alison, were kidnapped and brought to the dollhouse. The Dollhouse consists of thirteen (known) rooms and an electrical fenced in "backyard."
It is located in/under Tyler State Park. Interestingly, this park is in Bucks County. If you recall, this is where Toby got a job before being revealed as a member of the A-Team.