Deep below the streets of London, something is growing in tunnels that once kept people safe from World War II bombs. One hint: It’s leafy.

Growing Underground is a company that makes “kilometer zero” eating possible in London, by growing salad in LED-lit, underground factories right beneath the customers’ feet.

The Growing Underground farm sits 100 feet under Clapham in South London. It uses hydroponics and low-energy lighting to grow salad, including mizuna, watercress, Thai basil, radish, pea shoots, mustard leaf, and red vein sorrel. They grow year-round on racked beds that look like warehouse shelving. Best of all, the process uses 70% less water than regular surface farms.

Being underground has many advantages. One is food miles, or the lack thereof. Transport makes up a significant proportion of the cost of food, both financially and environmentally, so growing in a city center cuts that cost almost to zero. An old bomb shelter is also pest-free, as well as weather free, and there’s never a frost. That means no pesticides. And because the farm is hydroponic, all the nutrients remain in the tanks, instead of running off into the soil and then into rivers. The project is also working on carbon neutral certification.

Growing Underground has the help of chef Michel Roux, Jr., which no doubt helps sales to London’s restaurants, which are the main customer for the salad right now.

Abandoned underground tunnels seem like a great place from which to feed cities, but not every city has a subterranean labyrinth to exploit. Excavating from scratch would kind of defeat the purpose of such carbon-neutral, low-impact schemes, but there are alternatives. In Tokyo, one designer wants to float hydroponic greenhouses on the ocean next to the city.

Another farmer grows salad inside a house, and in Hollywood there’s a fast-food chain that grows salad inside its restaurants. Given the advantages, it seems that hyper-local salad will continue to grow.