In Germany’s Black Forest, the country’s largest theme park is making a splash with a vast indoor complex of 17 water slides, plus a ‘mythical’ island, ‘rivers’ and ‘caves’ open year-round

I’m ushered into what looks like an upright glass coffin, told to fold my hands across my chest in the classic corpse position – and then push a green button. I’m wondering exactly what I’ve got myself into when the trapdoor falls open and I plummet into a tube of fast-flowing water. It’s up my nose, in my mouth; I can’t see and can hardly breathe for a few tumultuous seconds before the gradient of the water slide reduces from vertical to merely steep and I’m propelled around more bends and spat out at the bottom. I feel like I’ve been flushed down a toilet.

The Vildfål is one of the more extreme experiences at the new Rulantica indoor water park, which opened on 28 November. Half an hour’s drive north of Freiburg im Breisgau in south-west Germany, it’s next to Europa-Park, the country’s largest theme park. Both are owned by the Mack family, a dynasty of entrepreneurs who have been enticing visitors to this corner of the Black Forest since 1975. In building the €180m Rulantica, the family has made its biggest single investment to date.