Not much is left of Black Castle an Anglo-Norman stone fortress dating from 1176, but in its day it had an eventful life frequently being attacked by the Irish and sometimes occupied by them.
All that is left are the south-east corner and south-west corner tower standing like decayed teeth on the headland above Wicklow harbour. There are fine views from here along the coast and across the town, and it is a good spot to sit and watch the activity in the harbour below.
If I remember rightly there is a coast path round the headland to join the Wicklow Head stroll.