Curl up under a sunny window with a good book. And a cat.
Home health care professionals recommend that shut-ins who can't get out sit with an arm in front of a window, preferably facing south or towards the sun at whatever time of day that is, for as little as an hour a day. Even this little bit greatly improves the body's production of Vitamin D.
The glass in the window blocks the UV portion of sunlight from getting through, so you’re not really getting the full benefits. Might be good to fight depression, but it’s not going to help you get your vitamins.