This is the nesting ground for the Harpies. The only way to currently get there is to fight a harpy and lose or surrender.
After they have their way with you, you wake up at night and have to try to escape.
Spoilers! Click to reveal:
-Move over to the bottom right corner and you will find small bones, some of them look sharp.
-Continue to use the bones to cut your bindings
-If you hear sounds coming from the nest, you need to go back to the middle of the harpies and pretend to sleep.
-Repeat until free.
- Then go to the bottom of the map and climb out.