Shining South is one of my favourite regions of the Forgotten Realms. It's not completely overblown and overdesigned like the Sword Coast, but you've still got a bunch of halflings, half-drow, wizards, merchants, barbarians, and a nice balmy weather. You've got the Desert of Desolation right north, Zakhara not far to the south, Celts to the east and then bigass mountain ranges even farther from that, and Jungles of Chult to the west. A great place to start a sandbox game, I think, with things to do no matter which way you go.
One of the first adventures I ever ran started from here. You had a prestigious cooking contest among the halflings of Luiren, and weird stuff started happening, with contestants being indisposed and their recipe books and ingredients disappearing. Turns out one of the halfling chefs was a drider in disguise, who wanted to win the competition just so he could drop his illusion at the end and laugh at their sudden revelation. Ah, good times.