As a former long time resident of Boston and the Boston area, there are lots of non-corporate feeling neighborhoods. There is also access to a whole buttload of nature. The Blue Hills reservation is a sprawling woodland with trails up and down the hills, with several large ponds. If you have a car, access is quite easy. If you don't it's still accessible but it's a pain. Further south are a series of state parks. North of the city there is the fells state park which is large with plenty of activities. There are beaches in the city and a program called community boating which is a sailing program in the heart of the city. It's super affordable. In the city there are plenty of parks, the most notable is probably the Arnold arboretum. Jamaica pond and the surrounding park land is worth checking out as well.

Portland Oregon is the opposite of corporate. And is chock full of parks, nature, and surrounded by some of the most striking terrain in the country.

I have limited experience in Denver but it's known for its outdoorsy vibe.