Source: ArenaNet Blog
The ArenaNet Audio Team drove down to Satsop, Washington - to record sounds using a site of a nuclear power plant that was never completed.
Using the cooling towers, which stood 500 feet high, they would make noise and record the impulse responses needed to generate the reverb they want in new sound effects.
The reactor building has several more types of rooms where they experimented getting more sounds, many of which sounded pretty scary.
The team went the extra mile, or literally over 1/5 of a mile, to blast sounds from a PA speaker, down to a 1350 feet tunnel that connected two cooling towers. There they achieved reverb times of 45 seconds at RT90.