There are two denuded Iron Age hillforts perched within woodland upon the eastern flank of Allt Lwyd. According to Coflein:
NANT TARTHWYNI [WEST ENCLOSURE] – SO08941944:
‘The subrectangular hillslope enclosure at Nant Tarthwyni west measures about 63m by 55m. It is defined by vestiges of a bank and ditch, with an entry facing downslope (to the east). A second enclosure lies 60m to the east.‘
NANT TARTHWYNI [EAST ENCLOSURE] – SO09111951:
‘An oval hillslope enclosure, about 75m in diameter, defined by the vestiges of a bank and ditch with an east-facing, downslope entrance, having a roughly concentric bank and ditch about its southern perimeter’.
Perhaps not worth a specific visit for archaeology alone, but the landscape, my friends, the landscape! Combine with a visit to Carn Pica and enjoy some serious mountain views, too.