Tree Fort

The Tree Fort is Finn, Jake, Beemo, and Neptr's home, and where they can usually be found when they aren't adventuring. It includes a living room, a bedroom, a kitchen, a pond, a well, and a wide look-out view.One of the the reasons Finn and Jake built and live in the tree house at such a young age might be because of the fact that Jake's parents died.

Living Room
The living room is furnished with a brown colored couch, several long tables, and a large monster-skin rug. In the corner there is an old phonograph and what looks like a wood burning stove with a pile of kindling next to it. In the episode "My Two Favorite People", Finn and Lady Rainicorn play video games on Beemo in this room. There is a clock on the wall that says, "Finn and Jake Timeless." The Living Room is next to the Kitchen.

There appear to be two living rooms-- one with a long brown couch, round red couch, and cooler; and the other with a purple chair and monster skin rug. The rug room is loacted one floor above the couch room.

Finn's Bedroom
Finn's room is over the living room and is accessed by a ladder made of planks nailed into the Tree Fort's tree's trunk. On Finn's bed is his mummy style sleeping bag on top of many pelts of various evil-looking furred and scaled monsters, assumed defeated by Finn himself. Finn dislikes worms crawling on his bed, as shown when he threw a book (possibly The Enchiridion) at the worm. Next to the bed is an end table with what seem to be a mug and a rusted muffler on it, and beneath the end table is what looks like a large magnifying glass. Over the head of the bed, the jaws of a very large shark are hung on the wall and a spiked mace hangs from the ceiling. The skin of some unknown six-armed beast lies on the floor as a rug. A large tree limb growing through the room has an old battered desk on it and in the intro has Beemo set on it. They apparently keep a cricket beside Finn's bed in a jar as seen in "Her Parents."

Jake's Bed
Jake sleeps in an open drawer of a cabinet, which also holds his viola, a picture of Lady Rainicorn, books, bones, and some of his other personal possessions such as a mug which looks to hold milk, ties, and a locket of some kind.

Cave
A small cave is built into the tree fort on its back side. The cave is full of tools, and in the episode "What is Life?", Finn builds Neptr there.

Attic
The attic is seen in "Rainy Day Daydream". There are the initials "AT" (that presumably stand for Adventure Time) carved into the tree, and a rug with various items such as candy and books. There is also a picture of Lady Rainicorn near the rug. It seems to be very dirty, presuming that nobody cleans it. Seemingly, the only way to get to the attic from the weapon room (the branch directly below) is by climbing into a bucket and using a pulley system to haul the person or objects up. Otherwise, using the bridge which connects to the living room will grant access to the attic. It seems to be an abandoned area since there are only a few items that are useful. However, it apeares that Finn and Jake do use it sometimes. It also appears in Go With Me when Finn was talking about Princess Bubblegum hating him.

Yard
The yard has several features including plants, a pond, a well, a yurt (the round hut structure), a mechanical device that might be an electrical generator, and a vegetable garden in the back.

Weapon Room
The Weapon Room, as its name suggests, is a room that stores weapons. It has a large gauntlet, small gauntlet and a small bomb that resembles a nuclear weapon. So far, it has only appeared in Rainy Day Daydream. It also has a bookcase and a chair with a pillow, and there is a desk with a notebook near the large gauntlet.

Boat
Seen mostly in the episode Slow Love, Finn and Jake keep a boat as a type of look out view at the very top of a branch at the top of their Tree Fort. It has a umbrella and other small objects in it. It also appears in Power Animal at the Roof Party.

Trivia

 * According to creator Pendleton Ward, Finn and Jake built the tree fort themselves, although the tree was originally owned by Marceline, as seen in the episode "Evicted!".
 * According to Finn, Science Cat and Shark appear here at 4:00 P.M. everyday.
 * On a clock hanging in their tree fort, there's a picture of Finn and Jake on the hour and minute hands (respectively), surrounded by the words: Finn and Jake--Timeless.
 * On the wall above the couch, (best seen in "The Jiggler" and in "Rainy Day Daydream") there is a ripped picture of a seemingly naked woman. However, according to Natasha, "It's not a naked woman, it's a woman in a crappy snapped bikini"
 * The Tree Fort is the only tree in the Grass Lands.
 * Finn and Jake keep piles of gold coins, gems, and other treasures in their house that appear near the door in "When Wedding Bells Thaw" and other episodes, ironically, in "Wizard", when Finn thought he had to pay for the last magic lesson, he apparently said "You can't do this to me man, I got no money!", though he could've meant money that he thought he needed to bring along in the first place.
 * A few characters have paid a visit to the Tree Fort: Ice King, Marceline, Donny, Lady Rainicorn's parents: Bob and Ethel Rainicorn, and Lady Rainicorn.
 * In some episodes like "Slow Love" and "Guardians of Sunshine" the Tree Fort is nearly destroyed but then rebuilt.
 * The treehouse as seen in Business Time is completely different from the regular build in later episodes. This is likely due to the episode's original sneak-peak airing, during which the treehouse design was apparently unfinished.