Everything is mounted on masonite cut to a standard size. Openings are placed in such a way as to make the set fairly modular and simple to expand upon.
The first piece is the entrance: a cave with several chambers to break up the action a bit.
Insulation foam and bark from the yard.
The top can be removed to allow access to the tunnel leading into the caves.
The caves within. I've included a small water course running from the back of the caves out through the entrance.
Next, the inside of a barrow. The circular pits will contain the remains of warriors long past.
Further updates as progress commences.