Stonehenge is an iconic and mysterious English landmark, but it's not the only place to attract the interest of local archaeologists. Nearly 100 stone monoliths have been discovered at a site called the Durrington Walls, about two miles north-east of Stonehenge. For the average visitor, there's little to see at ground level -- just the grassy remains of a sloping bank. But with ground-penetrating radar, researchers have mapped the area and discovered evidence of up to 90 stones three feet underground. Around 30 remain intact, measuring up to 4.5 meters tall, while fragments of a further 60 lay beside them.