Dún Laoghaire is compact and easily walkable. The DART station, George's Street, the harbour, and the seafront promenade are all within 10 minutes on foot of each other. Joyce's Tower at Sandycove is about 20 minutes walk south along the coast path.
The coastal walk from the East Pier to Sandycove — and beyond to Dalkey — is the most pleasant way to get around. The DART stops at Sandycove & Glasthule station, cutting the return trip if you don't want to walk both ways.