One of the few standing Roman lighthouses and a labyrinth of tunnels are a couple of the secrets at this historic castle.

A 300-year-old tea shop that brought tea to the English people, not to mention the Queen herself.

A mysterious shape catches the eye in this 16th-century painting.

Originally meant to hold a statue of King William IV, this support sat empty for years. Today, it hosts a rotating cast of public artwork.

Formerly known as Saville Theatre, this mid-20th-century entertainment hub includes an ornate frieze.

A labyrinth hides in plain sight at each of the city's 270 Tube stations.

Revel in the Victorian splendor of the world's oldest eating establishment inside a museum.

This macabre painting of a Shakespearean scene looks like something out of a nightmare.

This stone commemorates the island's launch into international aviation.

This massive collection of British military artifacts includes the heartbreaking personal letters of the men in the trenches of WWI.

Richard III supposedly disposed of his nephews' bodies here in an effort to seal his claim to the throne.

The watery entrance for condemned prisoners heading to the Tower of London is still visible along the Thames.

Tucked away in the Tower of London is the weapon once used to execute high-profile prisoners.

An architectural oddity hides in plain sight on this iconic London bridge.

The "Black Arch" guards the entrance to the picturesque Glens of Antrim.

Commemorating the landing of William of Orange with his European army on their way to the Battle of the Boyne.

This castle once belonged to one of the most prominent families of medieval Carrickfergus.

This short bridge is the only thing connecting a tiny Irish island to the mainland.

Northern Ireland's Brobdingnagian stepping stones.

This tiny train shuttles passengers to one of Northern Ireland's most spectacular sights.

Step into Narnia at this small park featuring statues from "The Lion, the Witch, and the Wardrobe."

Belfast's namesake river still winds below the city center, hidden from sight.

This massive monument has been telling the time for 150 years—at a slight angle.

The only monument to name all of the passengers and crew who died on the RMS Titanic.