Simplify the following text for a Grade 10 native English-speaking person.
Original: In Sikhism , it is one of the most significant holidays in the Sikh calendar , commemorating the establishment of the Khalsa at Anandpur Sahib in 1699 , by the 10th Sikh Guru , Guru Gobind Singh .
Simplified: In Sikhism , it remembers the creation of the Khalsa at Anandpur Sahib in 1699 , by the 10th Sikh Guru , Guru Gobind Singh .