Around 20,000 people gathered on Sunday to the neolithic site, located on Salisbury Plain in Wiltshire, to watch sun-up on the year's longest day to mark the astronomical phenomenon.

The ruins, located just five kilometers from Stonehenge, likely laid the groundwork for religious rites celebrating the longest and shortest days of the year

Dave Hamilton, author of a new guidebook to the weird and curious, shares some of the less-known places to celebrate the longest day of the year