Not suitable for buses says a sign on the toad to Cwm Bychan. They're not lying: it is a long, windy, narrow road, but what a painfully beautiful place it leads to. The Roman Steps, whoever made them, are a wonderful footpath, taking you high up the hill very quickly but with little apparent effort. It is possible to leave them and head for the summit a short distanced before the col where a faint path follows a wall off right up a gully. But I carried on to the col and a bit beyond whence a less faint path leads up to and round Lln Du and up to a wall above it.
A path follows this wall (staying on the Lln Du side) south west till there is a left branch leading up the southwest ridge of Rhinog Fawr. From here I followed the main path down the SW ridge. This leads to a ladder stile by a prominent cairn. From here I was able, by keeping my wits about me, to stitch together an intricate way down to Gloyw Lyn that kept some kind of a path underfoot most of the way. A faint path follows the East Sid of the lake. From its north end a good path leads down to join the Roman Steps path not far from he car park. This is a wonderful walk through an amzing landscape that I would very happily do again and again.