From the World Heritage inscription:
The oasis of Bahla owes its prosperity to the Banu Nebhan, the dominant tribe in the area from the 12th to the end of the 15th century. The ruins of the immense fort, with its walls and towers of unbaked brick and its stone foundations, is a remarkable example of this type of fortification and attests to the power of the Banu Nebhan.
Getting to the Bahla Fort is pretty easy to do. It is a short drive from Nizwa, which is itself an easy 90 minute drive from Muscat. However, the view you get in this photo is about as much of the fort as you are going to see for the time being. They are renovating the fort so you can’t go inside. There are no signs or anything set up around the fort for tourists. If you are in Nizwa it is probably worth taking a look as it is so close, but a much better experience can be found at the Nizwa Fort.