Most visitors hit the Tiergarten by walking through it, which is fine until you realize the central axis (Straße des 17. Juni) is six wide lanes with the sun overhead and a tram-track median. The real shade is along the east edge, where the lindens hit critical mass against the old embassy walls.
These three keep you under canopy from the moment you cross out of Mitte until you arrive at whichever bench you wanted. We re-route around the Sunday flea market when it spills onto the grass — that’s a Stay Cool behavior, not something you do manually.