The narrow-gauge Welsh Highland Railway runs the 25 miles from Caernarfon harbour through the heart of Snowdonia to Porthmadog on the south coast. The full journey takes around two and a half hours each way and climbs through some of the best mountain scenery in Wales — past Beddgelert, around the flank of Snowdon itself, and over the Aberglaslyn Pass.
Trains are pulled by Garratt locomotives, distinctive articulated steam engines with a boiler at each end. The Caernarfon terminus sits just below the castle. Most travellers do a full return as a day trip; you can also break the journey at Beddgelert, walk in the hills, and pick up a later train back. Services run mostly between March and October.