Complex sentence: It is held annually during the first weekend of August somewhere in the environs of Moscow, Russia, since 1999 (open air since 2000) to this day with the exception of 2007.
Split into simpler sentences: It is held annually during the first weekend of August somewhere in the environs of Moscow, Russia. The festival is held since 1999 (open air since 2000) to this day with the exception of 2007.