Sean's Bar sits on the west bank of the Shannon, just down from the castle, and holds the Guinness World Record as the oldest pub in Ireland — and possibly the world, with verified origins around 900 AD. The floor slopes unevenly, the walls bulge with centuries of accumulated material, and the bar itself is barely changed from what you might have found here a few hundred years ago.
It's not a tourist trap. The Guinness is poured properly, the barmen are unhurried, and the clientele is a reliable mix of locals and curious visitors. On summer evenings the session musicians come in and the narrow interior fills quickly. The pub was once called the Inn of the Ford — Athlone's strategic crossing was the whole reason it existed.