"Adventure destinations that slip through the cracks"
https://news.ycombinator.com/item?id=7762095
From the submission title I figured it was just the usual travel spam, but after looking over the site and not finding you selling anything, I left it unflagged. I only visited the site to make sure it was spam before flagging, so it was a close call.
Though adventuring sure sounds like fun, unfortunately, I'm not in your target demographic.
I really don't know how to reach your desired demographic other than the obvious methods (SEO, A-B testing, cross-promotion with related sites/services, contributing to related forums, gathering email addresses of interested people for mailings, ... and just about everything else patio11 regularly tells people to do).
What kinds of things have you tried so far?
I imagine there are some interesting case-studies from people who frequent HN.
https://news.ycombinator.com/user?id=patio11
Also, there's plenty of previous HN discussions on niche targeting:
https://hn.algolia.com/?q=niche#!/story/forever/0/niche
As for the cross-over between hikers and hackers, I've seen the OpenBSD developers self-described as "A hiking club with a hacking problem." Nearly all of their main hackathons involve a hike of some sort.
If you don't know what those things are yet you don't have a niche.
And maybe you don't actually want a 'niche' in the traditional sense — see http://unicornfree.com/2011/niches-are-for-suckers
An acquaintance of mine used this for reaching some pretty specific niche, like males from a specific country, in a specific age range who like some type of cars.
He said that it worked better than other online alternatives, but as always YMMV.
Best advice ever - Be your own customer!