Below is our standard Adventure Fort which is based around 4 towers with 3 interconnecting bridges.  Under the bridges we fit full height palisades to make the fort truly impregnable; while the defenders can access the elevated tower decks (1.5m) via ladders, a scramble net and a rock wall. The towers on the fort have the option of standard or battlement walls on the top and are completed with 2 walls on each at ground level to keep marauders at bay.

Or if you want to maximise the internal area we can put the access climbs on the outside instead.

Alternatively you can adapt the adventure fort to your own requirements: you can make it into a different size or shape, increase the floor area of the towers, add more climbing features, and of course increase the fort size at a later date.