Located a short trot inside the edges of the Everfree Forest, if trotting down the west path of Ponyville past Fluttershy's Cottage and keeping straight. It's between Foggy Bottom Bog and Zecora's Hut.
There are a few more other forts like this one also built by Dreamer that are skills he learned from years of camping in his childhood and growing up. This one is proably his best one so far and can take a day for him to build one. The others are located around other cities in Equestria during his recent years of traveling in order to save some bits, searching for a city to live in and are probably still standing and look quite similar.
This one fort in the Everfree Forest was constructed in early December by Dreamer in a decent meaner well enough to keep heat in. It's just big enough for a pony to crawl in on the ground and extend legs out. It has a flip up door hatch and a prop. It's first finished rendition was a frame of branches and large thick stalky leaves torn in to strips and wrapped tightly around the skeleton of the frame. When temperatures dropped and kept snowing he spent an entire day revamping the fort with thicker limbs on the frame and a few layers of mud and barrier of woven leaves over it and added a vent to cut down on the moisture inside when sleeping. It's finished design is very strong and should hold up well in a blizzard.
A few yards away behind the fort is an interesting tree where he thinks might have been his pet squirrel Whistler's old home before moving to the Treebrary branches. This is the spot where he befriended him and noticed there might be something inside of interest which is now being looked at by two specialist ponies, the tree is very tall with the top broken off and few limbs except for one prominent thick limb high up with a hole at the base leading in to the tree.