The building is basically a ruin. There is a tattered Crimson Cross flag with some stone rubble. The building was probably torn apart when The Sands spread over it. Inside there is virtually nothing but a layer of sand and some signs written by Verigan Antioch.
There are some 'sandstone trees' around Lastwatch Hold. They were possibly made by the advancing sand covering the trees and turning them into sandstone.
It is unknown what Lastwatch Hold looked like before it was overrun by The Sands. However, the image was made slightly clear in "Shadow of Israphel" Part 41: Far From Home during Professor Webley's flashback. It showed he and a group of people from Lastwatch venture into The Desert before the building was overrun. However, this only showed a fraction of the building.
In "Shadow of Israphel" Part 35: Lastwatch Hold (Minecon Special!), after going through the Hellgate, our heroes arrive at night and find Lastwatch. They do a short investigation of the area and read a few signs. They learn from Knight Peculier that Lastwatch was the base operations of the Crimson Cross before it was overrun by The Sands.