This is the 9046th most frequent Turkish word.
tesisin
"Tesisin" means "the facility's" or "of the facility" in English.
Here 'tesisin' is the possessive form of 'tesis' (facility) indicating ownership, showing that the opening pertains to 'tesis'.
Tesisin açılışı bu sabah gerçekleşti.
The facility's opening took place this morning.
In this instance, 'tesisin' is used to suggest relationship or belonging, demonstrating that the capacity is in relation to 'tesis'.
Bu tesisin kapasitesi 500 kişidir.
The capacity of this facility is 500 people.
The sentence uses 'tesisin' to describe spatial relationship, implying that the gym is located within the 'tesis.'