I'm going to tell my girlfriend and friends it was stupid to go to the beach/nature/hikes and that they should stop asking me to go with them
That sounds pretty mean. Why do you think its stupid to spend time in nature?
I don't like nature and I don't like going to the beach and I don't like that they don't understand that.
Even if you don't like travel, you shouldn't tell your girlfriend what to do. You should support her.
I'm going to be more vocal about how I feel.
It's fine to vocalize what you prefer to do when spending time with your girlfriend. However if you're demanding then she might be put off. Why not just compromise instead and spend some time in nature but also ask that you get to do the things you like to do as well?