This was an "L" shaped tower house. The gate house in the foreground is what is left of the curtain wall. The stones which made up the corners and opening of the tower have been pillaged to be reused in newer buildings.
Tradition says the fourth Earl of Crawford built the tower house between 1446 and 1453, however, it is believed that the fifth Earl actually built it. There are five floors and entrance was gained by a large staircase protected by a machicolation. That means they could drop things on attackers heads, such as boiling oil.