Constructed from the same Preseli Bluestones used on its ‘big brother’ at Stonehenge, Pentre Ifan, near Newport (Pembrokeshire) also shares the same sense of mystery about its true purpose. It’s generally considered to be a communal burial chamber, but no traces of bones have ever been found here. An alternative theory suggests it’s a more elaborate version of a standing stone and the builders were simply showing off their skill. Whatever the real answer, there’s no doubt Pentre Ifan is an impressive feat of ancient construction methods. The giant 5m-long, 15-ton capstone, precariously balanced on three uprights, has managed to remain in place for over 5,000 years.