After a few live shows in Europe, Opeth returned to work on their next album, with Porcupine Tree's Steven Wilson producing. "This time it was tough", Åkerfeldt said, "I feel pleasantly blown away by the immense result, though. It was indeed worth the effort." Wilson also pushed the band to use new sounds and production techniques. "Steve guided us into the realms of 'strange' noises for guitars and voice", Åkerfeldt said. Opeth released its fifth studio album, "Blackwater Park", on February 21, 2001. This release encouraged Opeth to go on their first world tour, headlined Europe and playing to a crowd of 60,000 at the 2001 Wacken Open Air festival in Germany.