Slightly bonkers continuous run down a Snowdon runoff ditch. Steep and continuous, and lots of fun apart from the walkin.
Park at a small layby about halfway between Llyn Dinas and Beddgelert from where a major footpath heads up towards Snowdon. Walk the boats in up this path as it climbs to meet the river (about 2km).
Rainchasers is best experienced as an app.