D.C.'s first central library was born out of a chance encounter with the philanthropist whose name it bears.

The most accurate timepiece in the world.

Fittingly, America's museum of architecture is itself a magnificently designed old building.

A painfully obvious spy house sits right across the street from the Russian Embassy.

A lovely aquatic park built by a one-armed Civil War veteran who made a fortune from lotuses.

During the Industrial Revolution this “Temple of Invention” was full of intricate miniature machines and gadgets.

One of the dwarven trees dates back to 1625 and survived the Hiroshima bombing.

A monument in Washington D.C. marks the spot from which all other roads were supposed to stem.

The United States Capitol's former columns still stand.

This historic mansion was built as a symbol of love between a husband and wife.

A railroad tunnel that, upon its completion, was considered one of the engineering marvels of the modern world.

The ruins of this Thomas-Jefferson-designed mansion have been left to crumble since the Christmas Day they burnt down.

A computer bug so primitive it was an actual insect.

A tiny monument to the unsuccessful attempt by Thomas Jefferson to place the prime meridian in Washington.