Complex sentence: With a maximum capacity of 30,000, the Wörthersee Stadium in Klagenfurt also joined the race; however, it would require the construction of a roof for the contest to be hosted there.
Split into simpler sentences: With a maximum capacity of 30,000, the Wörthersee Stadion, located in Klagenfurt, also joined the race of hosting the contest. However, the stadium would require the construction of a roof for the contest to be hosted there.