Germany
Like many cities you have virtually unlimited options for walking tours. We particularly loved Original Berlin Walks - Discover Berlin where you'll get a fantastic overview led by a very knowledgeable guide (ours was getting a PhD in history) of the entire city in about 3.5 hours. On the walk you'll learn about WWI, the 1920s, WWII, the Cold War, and modern era. Sites you'll visit on the way include the Brandenburg Gate, the Berlin Wall, Hitler's Bunker, Checkpoint Charlie, Nazi Air Ministry, Holocaust Memorial, the Reichstag (Parliment), Museum Island, the Bebelplatz (scene of the Nazi Bookburning), Topography of Terror, Neue Wache (War Memorial), among others. Basically you'll hit all of the "must see" places.
New Mexico | United States
New Mexico has a long and interesting history - from Native Americans living here for thousands of years to the Spanish Colonial era to the early US frontier to building the first atomic bomb - and this museum does a good job of explaining it all. Well worthwhile.
United States | Washington, D.C.
A United States military cemetery spanning 624 acres just outside of Washington, D.C., Arlington National Cemetery was established in 1864 and is the final resting place for over 400,000 American servicemen and women. The cemetery is a beautiful and moving place.
Peru
Machu Picchu is one of the most stunning places in the world. Likely constructed as an estate for the Incan emperor Pachacuti, the city of Machu Picchu was built in the middle of the fifteenth century. Perched improbably on a plateau among sheer mountains, Machu Picchu is astoundingly photogenic, but it's even more impressive in person.
Austria
This cathedral is a masterpiece of Baroque art. Its beautiful façade and large size is a centerpiece of the city: look for the beautiful green copper domes and twin spires.
United States | Washington, D.C.
Located about a five-minute drive from the Gettysburg visitor center and ten minutes from downtown Gettysburg, the Baladerry Inn is our favorite place to stay around Gettysburg.
United States | Washington, D.C.
Walk by many of the foreign embassies in Washington on a fun and interesting walking tour. Once known as Millionaires' Row, many of the large homes along this stretch of Massachusetts Avenue have been converted into embassies.
United States | Washington, D.C.
Alexandria's historic district offers cobbled streets, charming townhouses, beautiful waterfront, delicious restaurants, and fun bars. There are also a number of historical sites to visit.
United States | Washington, D.C.
The National Archives houses the United States's most important historical records, including the original Declaration of Independence and Constitution. Rotating exhibits highlight other important historical documents.
United States | Washington, D.C.
A fun, interactive museum exploring the history and techniques of espionage. Great for adults and kids alike, the museum has informative exhibits as well as activities that teach you what it's like to be a spy.
