where it's at

Also, where the action is. The key center of activity; where important things are happening. For example, He decided to set up his store here, convinced that this is where it's at, or I'm going into the brokerage business; that's where the action is these days. The action or activity in this phrase can relate to just about anything—financial, political, social, or commercial. [Slang; c. 1960]