The West Coast of Wales hosts a number of interesting narrow-gauge railways collectively marketed as       
"The Great Little Trains of Wales"  One of the longest trips is The Welsh Highland Railway (WHR; Welsh: Rheilffordd Eryri) this is a 25-mile (40.2 km) long, restored 1 ft 11+1⁄2 inch  (597 mm) narrow gauge heritage railway in the Welsh county of Gwynedd, operating between Caernarfon and Porthmadog, and is associated with the famous Festiniog railway
It passes through a number of popular tourist destinations including Beddgelert and the Aberglaslyn Pass. 
A full round trip from either end takes 6 hours with a 90 min stop at either end before returning 
The views are stunning and the photos do not do justice to the real thing. The galley below gives only a taster. The Line is worked usually by Steam using the South African Garratt regauged to suit the WHR 
Interestingly the K1 Tasmania Garrat was returned to steam to initially work on this line but the loadings now are well beyond its capabilities.