Mount Fortress, or Fortaleza do Monte, is overlooking the ruins of St. Paul's and is the home of the Macau Museum. There is a park on top, with great views of Macau.
It was built in the early 1600's and played a big part in holding off a Dutch invasion in 1622. It stopped being a military base in 1965.
Unfortunately the conditions weren't very good for taking pictures last time I was there with a camera. So I only have a few, and they are mostly overcast. I'll try to remember to take some better pictures on a future trip. But for now, here are a few of the better ones.
Fortaleza do Monte bell, Macau
Fortaleza do Monte, Macau
Fortaleza do Monte, Macau
Fortaleza do Monte canon, Macau
View from Fortaleza do Monte, Macau
View from Fortaleza do Monte, Macau
ruins of St. Paul's, Macau. A view from the Mount Fortress
ruins of St. Paul's, Macau. A view from the Mount Fortress