The Lost Woods Resort is a motel located somewhere outside Rosewood. Mona brought Alison here after her attempted murder, and convinced Ali to disappear and pretend she died. This was also where Alison went after Duncan flew her from Hilton Head. Also, It was formerly "A's" secret lair. The Liars visit this place because they thought "A" was following Alison here.
The girls find out about the Lost Woods Resort while combing through the contents of Alison’s bag that was left on Jason's porch.
That evening, they drive to the Lost Woods Resort and check into Room 1, the number on the postcard they found in Alison’s things. Hanna trips in the mud on the way to the room. Once inside the room, Hanna and Emily try to warm up while Spencer and Aria sneak into the reception once again to get a closer look at the guestbook.
Hanna decides to take a shower to wash off the mud. "A" enters the room and gets very close to Hanna, but by the time she gets out of the shower, "A" is gone. Hanna then discovers the door of the room has been left wide open. Meanwhile, Spencer and Aria discover Alison had checked in twice as Vivian Darkbloom.
The next morning, Spencer and Aria return the guest book while Hanna and Emily discuss their costumes. "A" watches them through a peep hole from the next room while they talk. When the others return, Spencer suggests they get out of there before anyone notices they broke in.
Later, Spencer comes back to the Lost Woods Resort with Mona. Something Mona said made Spencer realize that no one had checked into Room 2 since before Alison went missing. Spencer sits for tea with the innkeeper to distract him while Mona steals the key to Room 2 from behind the desk. They stare in stunned silence when they open the door.
The room is plastered with photos of all the girls, newspaper clippings, dolls, maps and blueprints, and many familiar items belonging to "A"; it’s "A's" lair. Spencer and Mona get a closer look at the items in "A's" lair. Spencer begins to notice the pieces of the puzzle falling into place. Mona offers Spencer a piece of gum. She declines, then notices that there is a gum wrapper inside of Alison's stolen diary. When Mona momentarily leaves the room, Spencer finds more clues pointing to "A" being Mona, including a bag of cashmere sweaters. And when Mona returns, she is wearing "A's" black hoodie and Spencer's suspicions are confirmed that Mona is "A."
After that day Maya St. Germain's body was found, the other girls returned to the Lost Woods to destroy the evidence which would get themselves and their loved ones in a lot of trouble, but the room had already been emptied. As result, Spencer has been visiting the Lost Woods Resort all through the summer to recreate it in her computer.
It is revealed that the Lost Woods resort is up for sale. This is unsurprising because the resort seemed to have few other guests besides 'A'.
Alison flashes back to the night she disappeared. After her attempted murder and rescue by Carla Grunwald, Alison left the hospital alone and Mona finds her walking aimlessly along the road. They go to the Lost Woods Resort under Alison's alias, Vivian Darkbloom. Inside, Mona suggests that Alison should let A think she's dead by disappearing. While Alison is asleep, Mona is seen in A's Lair (presumably in Room 2) next door. The next morning, Alison leaves Lost Woods dressed as Vivian and drives away while Mona watches on.