How about some crawling passages? So small narrow and winding passages (ventilation shafts) at ground level? For people who are even fatter than me, you could do this optionally or adjust the height: So 40 cm/crawl on all four or 100 cm simply crouching movement. Without controller movement this is certainly very immersive, exhausting and funny :-)
By the way: I'm still of the opinion that your game lacks a little challenging gameplay. So I do tasks like looking for keys or something like that. Otherwise I find the progress so far really good. Keep up the good work!