An Abandoned Rotterdam Water Park Is Now a Mushroom Farm

Mention Tropicana, the former subtropical swimming resort in the heart of Rotterdam, to any 80s kid and they'll spin you a nostalgic yarn of boisterous teenage log fluming, water bombs and underwater French kissing. The water park closed its doors in 2010 and has since become a burden to the owner and the city council. Locals have been left wondering what will happen to the place—will it be demolished and turned into fancy apartments, or become an unsightly entertainment centre with a cinema and a smattering of crappy chain restaurants?

If it were up to RotterZwam's Siemen Cox and Mark Slegers, the guys who rent the building on a anti-squat lease today, Tropicana would become something completely different—a showcase of urban farming and self-sufficiency. Cox drove past the abandoned pool a year ago and realised that it looked like a huge greenhouse. He'd just read Gunter Pauli's The Blue Economy and the idea of using coffee waste to culture mushrooms had captivated him. So, enlisting the help of Slegers, he went about getting a lease for the place to realise their new, green dream of running a metropolitan mushroom farm.

MUNCHIES visited the old aquatic paradise and got the lowdown from the shroom-obsessed twosome. They were real fungis. MUNCHIES: How easy was it to get RotterZwam going here? Siemen Cox: Well, actually that was quite easy, because who wants to work in an empty swimming pool? We traced down the owner through LinkedIn and within a week we had a tour of the place. Two weeks later we had the keys.

Why was Tropicana abandoned in the first place? That's a long story. The former owner went bankrupt in 2010 after a troubled period with reports of bad hygiene, assault and other incidents. Neighbours weren't happy with this place at all.

Oh dear. So how do you make use of the park for growing mushrooms? The place offers a lot of possibilities. People often imagine that we'd use the pool space itself for mushrooms, but, although we hope the main space will become a greenhouse in time, we don't. Mushrooms like diffuse lighting and damp—the pool is much too bright and dry. The dressing rooms and the basement are perfect, though. We fill the bags with coffee waste, mushroom spawn, bean peel and calcic, and use Tropicana's old clothing hangers to hang them. People sometimes call the mushroom bags sausages, because the way they hang reminds them of a butcher shop. A vegetarian butchers, of course.

How does the coffee thing work? Coffee grounds are a universal fungus base. Oyster mushrooms grow very fast on that, they're kind of aggressive and weed-like and it only takes them five weeks to grow. What we do in our stomach, the root system of the mushroom does outside—it excretes enzymes to break down the environment. It's basically like an inside-out stomach. They really like the coffee waste, although they wouldn't like coffee.

Waste is an important subject for you, right? Yes. We're building a completely new chain here that doesn't produce any waste. We collect coffee grounds from local coffee bars and transport it in our carrier bicycle—everything is produced and consumed within 3.7 kilometres. Our worms compost the residuals and right now we are also examining ways to extract the enzymes for making bio plastic or use it for bio fermentation, but from one waste product we're creating five new products right now—mushrooms, compost, worms, worm-tea [basically liquidised worm castings] and enzymes.

Worm tea, wow. Why are you so passionate about this? Cities like Rotterdam produce nothing but waste and commuters. This entertainment park represents that perfectly—we build things and, when we don't want them anymore, we need others to clean it up, to sweep up our garbage. That's not how nature works, though—in nature waste doesn't exist. In this building we hardly ever buy a thing, because every material or nail is already here.

How many mushrooms do you produce? The amount of oyster mushrooms we produce is changing very fast. We now produce 20kg a week and are up scaling to 50kg. Right now the demand from local food truck entrepreneurs, restaurants and bakeries is bigger than our supply, and, although we get lots of inquiries, we don't supply places outside of the city. We want to keep it local.

That sounds like good business. It is going well, and we like to help people in other cities to do the same with their coffee grounds, too. Given the amount of coffee that people in Rotterdam drink, there could be 10 places like this in our city alone. That's why we're launching a home breeding kit at the end of this month, because we feel bad about how much coffee grounds are wasted in people's homes. Navigating the city's waste issues are very interesting to us because The Netherlands want to reduce waste by 50 percent by 2020. Thirty percent of what people throw in their bins is organic and we're working on a new model to make use of what they're throwing away.

What might we encounter if we visited you a year from now? Oof, that's very hard to say. Plans with this park change every month and a half. We really hope an investor will come and see how this would be the perfect spot for an urban farm flagship. Look at the place! You could grow algae, build aquaponic systems, use the walls for vertical farming, purify rainwater in the basement, and so on. Although it has a shady history, most people still love this place. Every day people crowd and take pictures outside and we receive at least five emails a week from people who want to visit. Oh, and the odd group of tourists in their swimming clothes on the doorstep.