The castle and the walled town it anchors are the obvious draws, and a single full day in Caernarfon is mostly spent inside Edward I's walls — climbing the polygonal towers of the castle, walking the medieval ramparts, ducking into the small, irregular streets and pubs the English built around them. A short walk south brings you to the much older Roman fort at Segontium; the harbour and the bridge over the Seiont sit just outside the western walls.
Beyond the historical core, Caernarfon is the launching point for the Welsh Highland Railway into Snowdonia, the start of the Llŷn Coastal Path, and the Lôn Eifion cycle route. The town is small enough to cover in a long day; most travellers stay one or two nights and use it as a base for the mountains and the Llŷn.