Level for exploring dungeons

Sorry is this has already been answered, I tried to find a "Search" option in the forums and couldn't find it.

Anyway... sometimes I see dungeons -or whatever they're called- that says "Level 3, your current level is 2". After reading a bit I know that I have to achieve a higher level (researching the Adventure tech tree AFAIK) in order to explore those spots. But how do I know which techs will award me an extra level? I see some that could, or could not, be the ones I'm interested in, but it's just a guess based in the description text.

Thank you!