Cultra Beach is the kind of place most people drive past on the way to somewhere else. A small shingle beach on the Lough with a car park, a view across to the Belfast Hills, and almost no one on it most days. The planes coming in low over the water to George Best City Airport are part of the experience, there's something oddly calming about them once you settle in. Bring something to read and walk the shore.
The Ulster Folk Museum is a short walk inland if you want an hour of something structured afterwards. The museum is substantial and undervisited, covering centuries of rural and domestic life in Ulster with reconstructed buildings spread across a large open site. But the beach is the reason to come. It has the particular quality of coastal spots that belong to the people who live near them rather than to tourism, and that quality is worth seeking out.