"The rippling of the clean water over the rocks will follow you for a majority of this adventure," the organisers said in an invitation for the event taking place along the Soča river.

The Red Bull 400 events will, meanwhile, give runners the "fourth opportunity for a win on the most difficult 400 metres in the world".

Taking place on Saturday, the footraces will take the participants up the ski flying and ski jumping hills at the Planica Nordic Centre.

On Friday, the SLO100 running festival, organised by the SLO Trail association, will offer three gruelling races of different difficulties taking place mainly over the hills of south-western Slovenia.

It consists of a 50-km trail, a 100-km trail and a 100-mile trail for the best mountain trail runners.