I have been working in MidTown East since the beginning of the year, after having spent several years working in Chelsea. Working in a corporate 9-5 environment (even if it is in digital media), it's important to find some renewal within nature during the day. That was easy in Chelsea, as I worked right along the West Side Highway and could walk the pier, and I was only a few minutes away from the High Line.
But Midtown East is a different matter. It's mostly just tall office buildings. To keep sane, here are a few places I visit during the week (all links are to Google Maps):
Peter Detmold Park. Walk east on 51st St until you can go no further, then take the stairs down to the park. (There is also a bridge that crosses over FDR Drive). At the bottom, you'll find a dog park to the immediate left. Although the park itself is mostly just concrete with a lot of benches and some trees, I find it pleasurable to watch the dogs play. That alone feels Nature-y. You can then walk along the park for two blocks and exit at 49th.
Katherine Hepburn Garden. This is a very narrow, winding garden along the edge of Dag Hammarskjold Plaza, along 47th St between 2nd and 3rd Avenues. You can walk on the stone path within the park, or just walk along the side of it on the plaza, itself a comforting walk, as there are about four water fountains interspersed along the route.
Greenacre Park. I'm pretty sure this is a privately-owned public space. It is only open during the warmer months, and features a very powerful, very loud waterfall, as well as a brook to the side. Pretty much all stone. If you like water, it can be reassuring, although I find the waterfall to be overwhelming.