Torre de Belem, or the Belem Tower, is a fortified tower and UNESCO World Heritage Site. The tower was built as part of the defense system at the mouth of the Tagus river, and also acts as a gateway to Lisbon.
The tower is built on a small island, and is somewhat small when you consider this was a fortress.
There is a large courtyard with cannon portals throughout the exterior on the side facing the water, with the tower looming large on the side closest to land.
The line to get in was pretty long when we were there, and I’ve read that the interior is really nothing special, and somewhat not worth a visit. As we were kind of short on time, we just had time to admire the outside.