Her idea of a good time "outside" is hitting up a few stores and browsing for new home decor, whereas mine is going on a hike, camping, exploring national parks, etc.
This sounds patronising as hell. You sound a bit like you think you're better than her and I almost guarantee she has picked up on this. So what if she prefers window shopping? She has a nice time doing it, just like you enjoy your hiking.
We have a beautiful national park (famous enough that it attracts literal busloads of tourists) from Toronto literally 45 minutes away - a gorgeous 45 minute hike, followed by cliffs and a walking path down to crystal blue water with underwater caves to explore, secret swimming holes, etc. and she refuses to go with me.
She'd sometimes come, but would never really enjoy herself.
Your phrasing makes it you sound like you can't get your head around how some people just don't appreciate nature but some people just aren't into it mate, no matter how beautiful you think it is.
A little anecdote: I am 100% not an outdoorsy person; I hate the wind, I hate the rain, I hate being cold, I don't find much beauty in some hills and even when the weather is nice I'll just end up bitching about being sweaty instead. The outdoors and I are just not a good match. But when I visit family they always insist on dragging me to the (cold, grey) beach or up some hills, despite knowing I hate it, and I end up feeling resentful and pissed off and it's not long before we start taking swipes at each other. It's lose-lose and everyone would've been happier if I'd stayed at home. I've always been like this, since I was really small. I'm 25 now and still think the outdoors is shit. And that is fine. I bet she has at least one thing that you just don't click with, either.
If you drag her like my family drag me, she will end up resenting you. Honestly I don't really understand why you can't try and learn to enjoy it alone with the dog, find friends or family who will happily come with you instead, or find some kind of group/club you can go with. Your future kids will probably love having some quality alone time with their dad. I mean, if it means so much to you you're willing to end an otherwise happy 5-year relationship then go ahead, but it seems like a massive overreaction to something that doesn't really need to be a problem in the first place.