Under a glass sidewalk lie the remains of some of Manhattan's oldest buildings.

Amid the bustle and noise of the Financial District hides a secluded garden oasis above the city streets.

America's oldest Eastern European synagogue provided the immigrants of crowded Lower East Side tenements a space of sanctuary.

Detailed facade of a brownstone in Boerum Hill.

The church's remarkable frescoes incorporate Finnish artist Hugh Simberg's trademark themes of death and the supernatural.

A subterranean house of worship carved right out of the bedrock.

A lovingly curated curio shop in which the taxidermy wear newspaper party hats, and peanut shells are spread across every surface.

This endearingly discomfited urinating statue commemorates the sneaky pees had by us all.

An abstract monument to a symphonic composer.

A small island dotted with old, historic Finnish buildings.

No matter how many times this community-run sauna gets destroyed, it always rises from the ashes.

These 5,000-year-old cave paintings provide a glimpse into prehistoric Finnish life.

This medieval Estonian tower provides access to a series of tunnels that have been home to soldiers, punks, and fine art.

Only a fragment of this 15th-century Dance of Death survives today.

The oldest continuously operating pharmacy in Europe.

An empty relic of the Moscow Olympics crumbles away in Estonia's capital.

Relics from an era long gone, sit idle outside this Estonian museum.

A forest park outside Tallinn full of architectural and artistic curiosities.

This set of concrete chambers resonates according to different notes of octaves.

This disappearing geyser has been attributed to witchcraft, but really it's all about rainfall.

Historic slum of Tartu.

Mysterious craters may have been home to an ancient cult.

This remote sandstone cliff has one of the richest collections of Livonian petroglyph marks.

Latvia's symbolic mountain-shaped national library is home to millions of cultural tomes.