Rome's semi-secret peephole vista is also a former Crusader stronghold.

One of the tallest buildings in Iceland, and perhaps, the most visually impressive.

This eye-popping Icelandic crater lake is surrounded by red volcanic rock.

This fantastical waterfall is hidden in a cave located in a cracked cliff.

Rising from the sea like a stone monster.

The unique waterfall in Iceland's south features a backdrop of geometric black lava columns.

Each spring, a dreamlike carpet of bluebells overtakes the forest floor.

Beautiful Austrian natural history museum with carved ceilings and row after row of ancient taxidermy.

Baroque celebration of the end of the Great Plague of Vienna.

A tropical paradise just a short trip from the opera house is filled with beautiful winged creatures.

The beautiful baroque library of the Hapsburg empire.

The alpine falls where Sherlock Holmes apparently met his demise can actually be visited.

This is not only one of the oldest collections in Europe, but also possibly the most beautiful.

Caves famous for the dragon-slaying saint who lived there.

A lush indoor jungle fills this bustling Madrid transportation hub.

Madrid's romantically ornate crystal palace has been offering shelter to plants and art for over a century.

Gaze upon chocolate sculptures depicting everything from chariot races to Gaudí's famous church at this shrine to sweets.

Construction of Barcelona's iconic (but controversial) church is expected to be completed in 2026—a century after the death of its architect.

An icy lake tucked among jaw-dropping alpine panoramas.

Down a cobblestone alleyway is a museum dedicated to Romanticism, with a secret garden.

Egyptian Revival movie palace abandoned for decades and restored in 2013.

France's national museum of scientific and industrial instruments.

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

Large-scale contemporary artworks tower over fields and lurk in forests around a Jacobean manor house.