| Gyrn Ddu | |
|---|---|
 Gyrn Ddu (left) and Yr Eifl seen from the summit of Gyrn Goch | |
| Highest point | |
| Elevation | 522 m (1,713 ft) |
| Prominence | 386 m (1,266 ft) |
| Parent peak | Gyrn Ddu  |
| Listing | Marilyns in the British Isles |
| Coordinates | 52°59′40″N 4°23′01″W / 52.9945°N 4.3837°W |
| Naming | |
| English translation | black horns |
| Language of name | Welsh |
| Geography | |
| OS grid | SH 401467 |
| Topo map | OS Landranger 123 / Explorer 254 |
Gyrn Ddu is a hill near the northeastern corner of the Llŷn Peninsula in the community of Llanaelhaearn in the county of Gwynedd in North Wales. It forms the western half of a wider upland area, another significant top of which is the 510 m summit of Bwlch Mawr to the east.
The distinct northern top of Gyrn Ddu is Gyrn Goch, which attains a height of 492 m. The summit of an eastern top which reaches 491 m is crowned by a prehistoric cairn. To the southwest of Gyrn Ddu is the lower top of Moel Pen-llechog, which reaches a height of 316 m, whilst to the south is the 416 m flat top of Moel Bronmiod.