New York City has more museums than just about any other city in America. Some, such as the American Museum of Natural History, are huge. Others, such as Museum, which occupies a former elevator shaft in Chinatown, are no larger than a closet. New York also has its share of obscure museums—museums that might not make it onto your travel itinerary but are well worth the visit. Here are four of my faves.

The Museum of Sex

Controversial, coy, and undeniably erotic, the Museum of Sex teases and titillates visitors with a comprehensive look at the history, evolution, and cultural significance of human sexuality. No, MoSEX (as it’s amusingly called) is not for kids. But even the most sexually mature grownups will learn a thing or two from visiting.

Permanent collection items include art rom Keith Haring, period photography, and blow-up dolls designed to be companions. Rotating exhibitions have spotlighted the sex lives of animals, photographs of film star Linda Lovelace, and more. The museum has a bar and café, which is known for its sticky buns (seriously). Also of note: The museum store, which sells items such a packs of dirty fortune cookies. Ticket discounts are available online.

The Tenement Museum

The Tenement Museum

This fascinating museum tells the stories of the building at 97 Orchard Street in Manhattan’s Lower East Side, a tenement building that once was home to nearly 7,000 working-class immigrants.

In the most basic of visits, you can take guided tours of apartments that recreate immigrant life in the 19th and 20th centuries. But visitors also can go beyond the physical walls of the building to take a walking tour and explore the neighborhood and how it has changed. (One of these walking tours focuses on foods of the Lower East Side, and enables you to taste everything from dumplings to fried plantains, cream puffs and more.) Some days, there even are costumed interpreters playing the roles of past residents, answering questions in character about yesteryear.

Museum of Mathematics

Fractals and other graphical representations of math in modern life are front and center at this Flatiron District museum, which aims to bring math to life.

Most of the exhibits here are hands-on, making the museum a great destination for (older) kids. Some of the more notable interactive exhibits include an area where you can make mathematical structures with uncommon construction toys, and the Mathanaeum, where you can apply different operations to transform basic shapes into unique three-dimensional structures.

Viewfinder Tip: Visit museums mid-week to avoid weekend crowds.

Other visitor favorites include an area where you can create piling patterns called tessellations using unusual magnetic shapes, and, of course, a section where you can create fractals. The museum opened in in 2009, making it one of the city’s newest.

The City Reliquary

Located in Williamsburg, Brooklyn, this intimate museum and civic organization has a permanent display of New York City artifacts that paint a picture of the city’s past through time, and a series of rotating exhibits that spotlight certain eras in the Big Apple’s past.

An exhibit in the summer of 2014 spotlighted a man named Dick Power, a former Queens resident who was obsessed with racing bicycles and crafted hundreds of fine artisan bike frames. Previous exhibits featured donut shops of past and present, as well as the Coney Island Velodrome. The museum is open Mondays through Wednesdays by appointment and Thursdays through Sundays for walk-ins.

What sorts of museums do you like to visit when you travel?