I've found acroyoga or other variants of partner acrobatics amongst the easiest activities to get into a flow state. I think it's because there is lot of novelty, a high-perception of risk (although is actually quite safe), and a high requirement for coordination. I would describe it as literally forcing you into the moment. Whereas when I run, practice yoga, lift weights etc., my mind is elsewhere.
This is super interesting! I might have to see what the AcroYoga scene is like around town.
This may sound a bit weird, but sports with "mandatory flow" really appeal to me. Snowboarding being the canonical example I use when I talk about this. I'm by no means as expert snowboarder, and when I'm doing it I have to be 100% in the moment. The sport has a great physical feedback loop for me: if I allow myself to be distracted, there is an immediate violent reminder (as I wipe out). Krav Maga has this too, although its more bursty (lose focus during a drill, accidental hits happen)
