Starting with the terrain and making the training work to that is really the wrong way around.
You need to assess the demands of your event, explore how you build your fitness around those demands over time, in a progressive fashion.
When is your event? If it’s next year you need to be building the foundation of your periodised fitness now, not doing race-specific stuff.
If you want to do this properly, either get a Joe Friel book to understand training protocols and principles a bit more, or speak to a coach.
Sorry, that sounds grumpy – its not meant to ;)