The Old Fort was Drakortha’s 3rd base during The Ancient Worlds single player days. The 1st base being The Deadly Mines and the 2nd The Farm (now known as Euloria Estate). All bases were constructed during Minecraft Alpha.
The Old Fort was built inside an existing mountain with windows looking out and walkways running along the outside. There was also a large tower constructed on the top that reached beyond the clouds and hit the height limit. This was before map heights were increased to where they are today.
Drakortha built a long, 1×1 minecart track that ran from The Farm all the way to the Old Fort. It wasn’t until completion that he realized it was a waste of time and resources because his minecarts wouldn’t move without powered rails.
Eventually The Old Fort became the first spawn point for The Ancient World when it went public on December 14th 2011. The Shire was constructed in a field nearby.
A commentary on The Old Fort from Drakortha during Minecraft Beta is up on Youtube.