I found that the way that the sites have been nested was.......interesting:

The British Isles › South & West Wales › South Wales & the Borders › Pen y Crug › Twyn-y-Gaer › Mountain Centre 1 › Cefnbrynich › Mynydd Bach > Nant Tarw

`Mountain Centre I` is listed as `Mynydd Illtyd` (at SN976265) in the SMR.

For `Mountain Centre II` the SMR has `Traeth Mawr I` at SN963254 and `Traeth Mawr II` at SN964256.

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