Hi, would you help me with this topic?
I spent hours searching but I failed to find information I need.  
In my country we have many mountains and (naturally) valleys.
So We go hiking in the mountains and go camping in the valleys.
 (and not every valley  connected to the river.) 
 
Q: What do you do in your free time?
A1: I go hiking in a mountain, the mountain, the mountains. (not specific mountain)
A2: I go camping in a valley, the valley, the valleys.(not specific valley)   
 
1. Are those three used interchangeably or which is the best to use?
2. Do you actually go camping in the valleys? (not a campsite)
    Or do you more often go camping by the river in your country?
Thanks always ! 
PIA