Moses Gates's Hidden Cities: A Memoir of Urban Exploration is a wildly entertaining journey beyond barriers to find the off-the-radar places in locales around the world. Gates has some hidden places for you to explore on your next trip.

After writing Hidden Cities, I’ve gotten asked one question more than any other: some variation of “so – I’d love to see a part of a city that’s hidden and secret and unknown, but also, you know, safely and legally.” It doesn’t really work like that (in today’s day and age, excursions that are safe, legal, and interesting enough to be found in major publications usually don’t stay hidden and secret for too long), but there are a few off-the-beaten path destinations around the world where you can see the forgotten corners, hidden infrastructure, and underground tunnels of some of the great cities of the world in a safe and legal way - but also get your feet slightly dirtier than your average tourist. 10 of my favorites are:

1. Le Musée des Égouts de Paris (Paris Sewer Museum) - A wonderful, up-close way to see one of the most significant engineering accomplishments of the 19th century. Descend into the bowels of the city, and walk alongside an active part of the Parisian sewer system. The entrance can be found across the Seine from the Eiffel Tower, on the Quai d’Orsay near the Pont de l’Alma

2. Bunker-42, Moscow - If you’d have told me (or any American) in 1983 that in 30 years we’d be able to visit a Soviet nuclear-bomb shelter, I’d have thought you insane. But today, you can travel 65 meters below Moscow and see just that. Entrance is at Building 11, 5th Kotelnicheskiy Lane, Moscow.

3. G-Cans Storm Drain, Tokyo - If you’ve ever seen a commercial (most famously for Land Rover), TV show, or movie featuring a giant underground chamber with pillars hundreds of feet tall, chances are it was filmed in Japan’s massive underground water-retention chamber, G-Cans, located on the outskirts of Tokyo. Tours are twice a day, Tuesday to Friday, but in Japanese only.

4. Whitechapel Bell Foundry, London - Dating back to (at least) 1570, this is the oldest factory in the British Isles, and arguably the oldest in Europe. They still make the bells using the same casting process as 400 years ago. Both Big Ben and the Liberty Bell were cast here. Tours are Saturdays only, and book up well in advance.

5. Antwerp Ruien, Antwerp - Originally dug out as moats to guard the city during medieval times, the ruien were then used as an inland port and water supply system. Centuries later, these canals were covered and converted into sewers. In the 1990s the sewer system was reorganized, and today you can walk through the Ruien tunnels, which date back hundreds of years . Tours are in Dutch, French and English, but make reservations well in advance. Excursions leave from Suikerrui 21, near the City Center.

6. Capuchin Crypt, Rome - Descending into the crypt below the church of Santa Maria della Concezione, one can wonder who in the world came up with the idea to decorate six chapels entirely in human remains. Even the light fixtures are made out of bones. It’s been a destination for those interested in the macabre for centuries - the Marquis de Sade made a journey back in 1775. The Crypt is on Via Vittorio Veneto 27.

7. Basilica Cistern, Istanbul - Istanbul has hundreds of ancient water cisterns underneath the city – most of which are abandoned and forgotten remnants of Roman-era Constantinople. Some have been rediscovered, however, and three are currently open to the public. The Basicilia Cistern, about 500 feet from the Hagia Sofia at Yerebatan Caddesi 13, is the most easily accessed.

8. Atlantic Avenue Tunnel, New York - Opened in 1845, this rail tunnel underneath Atlantic Avenue in Brooklyn – often called the world’s first subway – was open for only a short time before rail locomotives were banned in Brooklyn and the tunnel was sealed. After laying dormant for decades, it was rediscovered in 1981 by a Brooklyn teenager, Bob Diamond. Tours were occasionally given by Diamond until the NYC Department of Transportation shut them down in 2010. Hopefully, a way to make the tunnel accessible to the public can be found again.

9. Cape Town Tunnels, South Africa - Built by the Dutch settlers in 1652, Cape Town was originally known as “Little Amsterdam.” Today, you can visit one of its now-covered canals. You enter through a cast-iron manhole at the foot of Table Mountain, and emerge at the Castle of Good Hope. Tours have to be pre-booked, and will be cancelled in case of heavy rain.

10. Puente Avellaneda, Buenos Aires - The original bridge from the Buenos Aires neighborhood of La Boca to the suburb of Avellaneda was an old type of bridge called a transporter bridge - only a few of which are left around the world. It’s now abandoned, but still standing. Next to this rusting structure is the newer Puente Avellaneda, which has a pedestrian path in addition to roadways, providing a beautiful view of La Boca. Careful though –the part of Avellaneda the bridge leads to isn’t very safe, and muggings have been known to take place on the pathway.