I'll be the odd man out and claim Baku. On paper it looks like a bunch of 90° corners, and you would be right. But, each one is different, with different track widths at entry and exit. Turn 1 has got to be the fastest 90 on the calendar. Turn 2 has a quite narrow exit. Turns 5 and 6 are basically a chicane.
The old city section is a serious challenge to get even close to right. I've run a hundred different lines through there and still feel I can improve. And the approach to 15 is blind, guessing your turn entry on the walls. The home straight is flat out, but the kinks can still get you. Overall a very difficult but fun lap when you get it right.