There are several parks where I take the dogs hiking, one is 5 minutes from my work which is great for after work or on a long lunch break. One is adjacent to my dad's house and one is adjacent to my mom's house. All three are never busy, I think I've only seen a small handful of people at all of them all combined over the years. All three are huge, the smallest is 80 acres. We do off-leash but only because I have great recalls on all three of my dogs.
For training, we got to the training center I teach at. I am up there teaching or working generally 5-6 days a week, so they get a lot of training time. During the summer, we go to local sports fields to practice disc. I generally only go to places that have sprinkler systems as the grass is always nice and soft (too many slips on slippery grass!). We have 3-4 that I frequent within 10 minutes of my house or work.
As far as swimming goes, there are a bunch of lakes with public access docks, beaches or rivers close by. Again, I have 3-4 spots I frequent in the summer.
We don't really do leashed walks. They are boring, I hate small talk with neighbors and my dogs get frustrated.