It's a sign of the times when major cities around the world open up nap cafes.

From Tokyo to London, Seoul to Paris, the list of cities opening up nap cafes has been growing in recent months, with busy, overworked and burnt-out urbanites welcoming the idea of being able to take a power nap in the middle of the day.

One of the newest additions is Madrid, which saw the opening of Spain's first sleep cafe earlier this summer, aptly called Siesta & Go.

Given the country's long-standing tradition of closing up shop for hours at mid-day to escape the summer heat, it makes sense that Madrid would be the latest city to adopt the trend.

For about US$16 customers can retreat to a private bedroom and squeeze in a power nap during their lunch hour.

The Zen Bar a Sieste in Paris also offers locals a quiet retreat in the middle of the bustling city, with massage chairs that invite guests to indulge in a snooze, and other services like foot massages, fish pedicures and Shiatsu massages designed to de-stress their guests.

In Seoul, South Korea, where employees work notoriously long hours, one of the leading cafes in the business is Mr. Healing, with 60 locations across the country, writes The Korea Times.

Be it a micro-siesta of 15 minutes, or a more luxurious one-hour doze, nap or "healing" cafes as they're better known locally, offer sleep-deprived locals a chance to recharge in the afternoon -- a service that has become increasingly popular for everyone from office workers to new moms.

Customers slide into massage chairs, bean bags or hammocks and close their eyes, waiting for Mr. Sandman to bring them a dream.

While the sleep cafe trend is firmly entrenched in South Korean culture, in other cities it operates as a working experiment.

London, for instance, has seen its fair of pop-up nap stations over the last few years, set up as promotional gimmicks from mattress companies and design companies.

Last year, Londoners got a Nap Station equipped with power nap pods, beds, free Wifi and coffee at the Old Truman Brewery. The year before, a design studio opened the Sleeperie pop-up, where guests could cocoon themselves in swinging red hammocks.

To mark World Sleep Day back in March, Nescafe Harajuku partnered with a bedding company to open a pop-up nap cafe in Tokyo in the spring.

At the end of their power nap, guests were given a cup of Nescafe coffee to get on with their day.