I was surprised to see Hindu temple in Nha Trang. Didn't know there's hindu influence in the country. Ponagar was a temple complex built in 8th century.
It's a bit outside the center, you can take a geab or bus No.4 from the beach to the temple.
The temple isn't that big, but nice if you go in the afternoon a bit before the closing hour, to avoid crowds and to enjoy the sunset and great view.
Temple is well maintained, you may find it not as impressive as the bigger ones you see in India, but otherwise it's interesting to take a look.
You can have a great view of the city from here. But do come before or after all the crowds, otherwise it won't be much fun I believe.