How about St Michans Church! The Church itself is very interesting, and then there are the Mummies for the non-squeamish!
Dublin Sketchers get together every Sunday afternoon in Dublin to sketch. We go to a different place each week. Check here before hand to see where we are off to. Come along if you fancy it! We start sketching from 2pm and meet at 4pm for a drink and chat. We are part of the global Urban Sketchers community.