Complex sentence: It is the retreat of the Eastern States Buddhist Temple of America, Inc. ("ESBT"), whose downtown branch of the Mahayana Temple (aka Mahayana City Campus) is located in New York.
Split into simpler sentences: It is the retreat of the Eastern States Buddhist Temple of America, Inc. ("ESBT"). The downtown branch of the Mahayana Temple (aka Mahayana City Campus) is located in New York.