Under the frequent clatter of trains passing overhead, a stretch of Tokyo known as Ameyoko hums with life. Bordered by Ueno and Okachimachi stations on the central JR Yamanote Line, the area offers just about everything — fresh seafood, vintage clothes, watches or, come evening, scores of office workers unwinding over drinks or dinner.

In a city as dense as Tokyo, real estate comes at a premium. As a result, train operators such as Japan Railways (JR) have long made use of the space beneath the elevated tracks they manage. These narrow strips host everything from bustling izakaya (Japanese pubs) and quirky boutiques to hotels, apartments and even nursery schools.

But not all of these spaces — even along the Yamanote, one of the world’s busiest train lines — are thriving. Some are used for storage or fenced off as back-of-house lots, and others sit vacant. Increasingly, however, developers are reimagining these under-track zones for what they are: untapped land in the heart of the world’s largest city.