Brussels - Not many people would list Brussels, 100 kilometres from the gloomy and windswept North Sea coast, as one of Europe's top scuba-diving locations.
That could be about to change.
'At weekends, it's amazing - we get divers coming up from Paris, they come over from the Netherlands, we even have groups flying in from Switzerland to dive with us,' Brussels-based scuba instructor Jean-Pierre told this correspondent as we strapped on our scuba gear.
But the attraction is not the kind of palm-fringed tropical beach or sweeping coral reef which divers traditionally favour. Instead, it is a swimming pool located unpretentiously on a suburban roundabout.
'We'll start by going down to 2.5 metres to check that you're comfortable. Then we'll go on down to 10 metres, swim through the tunnel and stop for a chat in the cave. If you're happy with it, we can then go all the way down,' Jean-Pierre said with a grin.
Not many swimming pools on Earth even have a 10-metre depth to go 'all the way down' from. But this is Nemo33, a legend among Europe's diving fraternity, and at 35 metres deep it is the deepest swimming pool in the world.
'I've heard that there are plans to build a 40-metre pool in Madrid, and there's some Arab sheikh who apparently wants his own one, but for the moment, we're the deepest there is. Shall we dive?' Jean-Pierre said, and turned his thumb down like a Roman gladiator.
Nemo33 is nothing if not impressive. Its 2,500 tons of fresh water are heated to a temperature of 32 degrees - as good as a warm bath - by solar power, and so clear that from one end of the pool you can see the bubbles rising like silvered jelly-fish at the other.
Broad metal steps lead down into the shallow end, at 1.5 metres deep a bagatelle for the serious diver. There, pairs of scuba enthusiasts - they never dive alone - stop to put on their fins and masks, so that the view from underwater is a forest of legs.
Beyond them, the floor drops down to 2.5 metres - ideal for beginners - and then, after a brief swim, to 5 metres.
At that point the pool divides. To the right, it drops away to a broad ledge 10 metres down, while to the left, it plunges into the Pit - a 12-sided shaft 35 metres deep.
'Go right and down,' Jean-Pierre signalled, and we kicked off the ledge. Diners in the Nemo33 restaurant waved at us through armoured windows as we drifted down the wall.
From the 10-metre ledge, a tunnel leads directly into the side of the Pit, like a scene from the Death Star in the first 'Star Wars' film. To either side, narrow openings lead into high-chambered caves, filled with air by the club's ventilators.
'Hot, isn't it?' Jean-Pierre asked as we surfaced for a chat in a cave decorated with fake stalactites. Indeed, with 32-degree water lapping around the echoing walls, the air was like a Turkish bath, so that it was a relief to slip back under water.
On any coral reef in the world, the most spectacular place is the drop-off - the point at which the shallow reef suddenly falls away and the diver swims out into the emptiness of 'the blue.'
Nemo33 does its best to duplicate that effect, as the white floor tiles in the 10-metre tunnel open out into the Pit.
On peak days it is so full of divers' bubbles that divers looking over the edge can only see their own reflections, distorted in a million rising bubbles. On quiet days, it is a dizzying blue chimney.
At any time, it looks like a very, very long way down.
We took our time. Jean-Pierre led the way, and we spiralled gently downwards past windows and camera attachment points, the hardware of the centre's underwater film studio.
At 30 metres, the gas in a diver's air tank is so dense that it becomes intoxicating. At the bottom of the Pit, we stopped to play slow-motion volleyball with a model submarine because it seemed like a good idea at the time.
When our dive computers told us that it was time to go, the surface looked a very, very long way up.
But Jean-Pierre knows his business. We drifted back up slowly, stopping to chat in sign language with other divers, and in time swam back over the 2.5-metre ledge and through the forest of legs.
Other divers, Belgian, French and Dutch, were clambering back up the steps and breaking down their equipment. More were attaching fresh air tanks in preparation for the evening's second dive.
Outside, the winter rain of Brussels lashed across the roundabout. Inside, warm waves lapped against the poolside.
Belgium may not be a tropical diving paradise. But for those who are in on the secret, the bubbles of Brussels could well be the next best thing.
Internet: www.nemo33.com
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