“You take a tour like ours to break down what might otherwise be a million-piece collection like at the Louvre or the Met,” said Stephen Oddo, a co-founder of Take Walks, a walking tour company that operates in New York and San Francisco as well as eight European cities, including London and Rome. “You could go with a guidebook or an article, but that’s very passive. With historic places, it’s always better to get context and richness delivered in person by someone who specializes in it.”

Mr. Oddo and his co-founder, Jason Spiehler, met while working in Rome, where Mr. Spiehler was a guiding tours at the Vatican. Together they founded Walks in Italy in 2010; in other countries the company now goes by Take Walks. The company offers tours like the Louvre in Paris at closing time, when traffic around the “Mona Lisa” dies down, and a full-day trip to three sites by the architect Antoni Gaudí, two of them museums, in Barcelona.

“In the last 10 years, we’ve seen a shift from larger-group, checklist-style, in-a-bus itineraries to smaller tours with guides that have a specific knowledge on a subject and can speak to that nuance,” Mr. Oddo said of the Take Walks tours, which are designed for 12 to 15 people. (Most museum itineraries run two to four hours and range $42 to $107; register at takewalks.com.)

For those seeking a more intimate excursion with an expert, Context Travel recruits archaeologists, art historians and professors to lead its tours, limited to six guests. In 2017, the private equity firm Active Partners invested over $5 million in the company, founded in 2003 by Lani Bevacqua and Paul Bennett, with the goal of expanding the company’s reach. It now operates in nearly 50 cities.

The company’s tours are not exclusively museum-based, but where they are, “themes range from connoisseurship, the currency of art, art theft (alleged or not), and generally the ostentatiously wealthy and conspicuous consumption,” wrote Nick Stropko, a marketing associate at Context, in an email.

In London, the British Museum tour explores the ethics surrounding the Elgin marbles sculptures, originally taken from Greece, which has requested their return. In Madrid, the Spanish Civil War tour visits historic sites related to the war, then goes to the Reina Sofía Museum to explore artists’ reactions to it, including Pablo Picasso’s “Guernica.” Context tours cost between $60 and $130 a person on contexttravel.com.

Covering more salacious ground, Shady Ladies Tours, which originated at the Metropolitan Museum of Art in New York in 2016, focuses on the courtesans, mistresses and beauties commonly depicted in art ($59 at shadyladiestours.com). The company has since expanded to cover “nasty women,” or women of power from ancient Egypt to American suffragists, and fashion and beauty across cultures, including scarification and nose rings, at the Met and other museums in Boston and Philadelphia ($28 to $54).