Diamond Hill is the walk that makes Letterfrack worth planning around. The upper loop climbs on stone path and boardwalk to a 442-metre summit, with views over Kylemore Abbey, the Twelve Bens, Ballinakill Harbour, and the Atlantic islands when the weather behaves.
The route starts at the national park visitor centre and is popular for a reason: it gives mountain drama without requiring a full hillwalking day. The upper trail is still a proper climb, so bring rain gear and do not trust a blue patch of sky for too long.