Geocaching is a great idea! And something my husband has mentioned in the past. I think we’ll have to try it!
Claire, if we don’t have some sort of an idea of what we’re going to do in the evenings, we end up watching a movie or something else on Netflix together. Not the worst thing in the world, but as a family who tries to limit screen time, I’m ashamed to say that over the last couple of months, we’ve reverted to watching something on the screen more often than I am comfortable with. If nothing is planned, the kids’ first question is, “Can we watch a show?” And then about 50% of the time, we’re saying yes to that because we have no idea of what else to do. The other 50% of the time, we’ll play a game or dh will take the kids swimming for a while, but as i mentioned earlier, swimming is about to end as the weather cools off.
When we lived in our own single-family home with our own yard, this wasn’t a big deal at all. There was plenty for us to do as a family, whether it was playing outside or even just my dh and I sitting in our swing and watching the kids ride bikes or draw with chalk on the driveway. In the winter time, we bundled up and played in the snow. In an apartment, it just feels different. Many people have dogs in our complex, us included, and the grass right outside of our door is a popular place to take dogs to potty. Fortunately, our apartment has rules about picking up after your pet, but the poop trashcan is in the plot of grass outside our door. I don’t want my kids playing in that grass, even if there’s no visible poop, ya know? 😉 There’s a playground at our complex, but my children aren’t interested in playgrounds anymore. Just the other day, ds10.5 told us that he felt like he was too old for the playground. 
Worse than watching a show or even being bored, is my own mommy guilt. I feel that I haven’t been intentional about our family time when the evening passes without us doing something together (other than TV) that’s fun and enjoyable for everyone. My children are older now (9 and 10.5), and reality has set in that they’re growing up too fast. So this is more about me needing ideas to create intentional times of togetherness and fun with my family than anything else.
Just yesterday, I was having a conversation with a friend. She had overscheduled her children and was spending hours of her day running to and from various extracurriculars and activities. She was exhausted and missed the free, unstructured time they once enjoyed. I told her I was in the opposite position. I feel like we have way too much time on our hands. The children and I have 3-4 hours a day of free, unstructured play time with which to pursue our own interests, take a nap, read a book or whatever we choose. After we eat dinner, there’s another 2.5 hours to fill, and none of us is interested in doing what we just did in the previous 3-4 hours. Does that make sense? So my friend and I both agreed that we were at opposite ends of a spectrum of time and we both need to find the balance.
@MountainMamma, Dh and I let the kids stay up untl almost midnight a few weeks ago for the meteor shower. We went out in pjs to a remote country road and waited for almost an hour to see the shower. We saw two very faint meteors, and that was it. We were all so disappointed! Still, that’s a great idea!
ETA: After contacting several nursing homes, I finally found one yesterday that would be happy to have our family serve one evening per week. We are all very excited about this!