Simplify the following text for a Grade 10 native English-speaking person.
Original: The `` Stars of the White Nights '' is a series of classical ballet , opera and orchestral performances at the Mariinsky Theatre and the Mariinsky Concert Hall .
Simplified: The `` Stars of the White Nights Festival '' runs from May through July at the Mariinsky Theatre and the newly built Mariinsky Concert Hall - one of the best-sounding halls in the world .