My motto regarding this is: You cannot immerse people if you do not set a baseline first. Meaning: Start without a theme so that people can settle in and not have wrong expectations after entering your park.
A great start after the first non-themed enclosure could be mountains for example. The area you are trying to set a concept for is elevated and has a few patches of steep un-used territories. Maybe look into marmots, mountain goats or ibex, a lynx, red panda, species such as are often impressive and can be quite active while maintaining an interesting starter of the adventure. Kinda like a world-mountain-trial.