The gorgeous library at Trinity College is home to remarkable treasures of Irish identity.

A giant roundabout made up of six smaller roundabouts can befuddle the uninitiated.

In all of the 29 years it was in operation, no prisoners ever escaped successfully... or so they claim.

A hidden three-foot-wide house separates these two regal churches.

This unusual lava tube spouts seawater during high surf.

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

Vermont's hills are alive with the sound of music at this historic hotel.

Unruly residents were housed in this one-person cell until the Black Maria arrived.

An underground magnet for ever-changing street art.

This pun was simply waiting to come to life, and one defense contractor made it so.

The vast, legendary catacombs hold secrets much stranger than stacked bones.

Perhaps the most spectacular grotto along the Algarve coastline.

These unusual rooms on wheels are holdovers from the 1960s.

One of few vertical lava tubes in the world accessible by foot.

One of the most beautiful bookstores in the world hides a neo-Gothic interior behind an art nouveau facade.

Building owners can take out tiles for free at this repository for historic building materials.

This eccentrically decorated palace is replete with grottoes, fountains, tunnels, and caves.

An ancient and majestic fortress that played an integral role in Portugal's road to independence.

This unreal Portuguese palace looks as though it's made from a pile of different castles.

Entire apothecaries are on display at this Lisbon museum, which explores the history of medicine.

This charming candle shop has been in business since 1789.

This Industrial Age architectural and engineering gem helps visitors and residents alike traverse Lisbon, “The City of Seven Hills.”

The world's oldest bookshop still in operation.

If a glacial river suddenly diving into a sheer chasm via a dramatic, multi-stage waterfall isn't peak Iceland, it's certainly close.