The Devil's Appendix (Welsh: Nant Clogwyn y Geifr)[1] is the tallest single-drop waterfall in Wales and one of the tallest in the United Kingdom.

It is a plunge style waterfall located on the Clogwyn y Geifr cliffs beside Twll Du in Cwm Idwal, Snowdonia, Wales.

It is formed where a small stream falls for approximately 305 feet (93 metres) to reach the slopes above Llyn Idwal.

[2] Depending on flow and the ambient temperature, it can be either an ice climbing route, a single drop waterfall, or a broken waterfall.

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