be where it's atused to say that a place or activity is very popular, exciting, and fashionable
[TahlilGaran] Dictionary of Contemporary English ▲
where it's at adv. phr.,
informal That which is important; that which is at the forefront of on-going social, personal, or scientific undertakings.
Young, talented and black, that's where it's at. We send sophisticated machines to Mars instead of people, that's where it's at. [TahlilGaran] English Idioms Dictionary ▲