The artist David Nash planted a circle of trees in 1977.

The U.K.'s first underground railway line is now a lively thoroughfare for runners and cyclists.

This former Welsh metal factory is now a lovely abandoned relic but was once one of the industry's world leaders.

The enormous earthwork sculpture honors the ponies that lived and worked in the old colliery.

A 600-year-old mini shrine guarded by a sword-wielding knight hides in a crumbling cliff face.

A group of glacial erratic boulders are improbably balanced on white limestone pedestals.

A little-known ruin with a convoluted history and a fascinating latrine drainage system.

These legendary stone steps were once used to haul coffins up the rockface.

A relic of Victorian grandeur hides beneath a busy South London road.

One of the oldest trees in Britain may have been witness to some of the country's formative moments.

A circle stone within a stone circle.

On October 17, 1814, a 15-ft. wave of beer ran rampant through the streets of London.

This huge concrete map of Scotland was built as a thank you gift from a Polish soldier.

A hidden tunnel leads to a medieval queen's shrine buried beneath a parking lot.

This macabre monument atop an ancient well gives a nod to a brutal episode in Scottish clan history.

Possibly the oldest living thing in Europe, more likely a pagan survivor.

Fantastically decorated underground chambers built in the 1760s.

A glorious pub known for a spiteful printing feud and its famous typeface lost—then found—at the bottom of the Thames.

This haunting stone chasm is a hotbed of mossy rock and English legend.

Eclectic final resting place of the controversial explorer.

Charles Babbage's proto-computer, painstakingly brought to life.

Below a historic English market town lies a secret underground city complete with kitchens, laundries, storerooms, and an underground lake.

A network of concealed passageways lies within a busy London Underground station.

This beautiful Victorian ironwork masterpiece was built to keep London from smelling like poop.