Everyone needs to relax from time to time. Adventurers probably need this more than anyone. Professional adventurers, that is a certain type of very specific mercenary who completes single jobs in small groups without generally engaging in large scale warfare (generally confined to the fantastic worlds of D&D and other such games where adventurers are the classical Other), spend a huge amount of down time drinking, eating, and resting. Like war, adventuring is essentially long periods of boredom punctuated by intense excitement.
In the earliest days of the hobby the tavern was also the de-facto place you could find someone looking for work, specifically adventuring work. What is the truth of this in history? Well, taverns (public houses before a certain time period), classically served as cultural and recreational centers. Generally, each evening in a village or town one person's house would become the "public house" and they would sell their own ale and this is where people would spend the fading hours of their nights before going to sleep and working from sunup to sundown the following day. The tavern continued this tradition while also serving as a stop-over place and eventually giving birth to places like Coaching Houses (which is what the traditional old school road-tavern-inn resembles more than anything).
My players constantly ask me where and how they can hire up hirelings and it only occurs to me now that I have a simple answer for them that doesn't rely on them sending heralds throughout the cities. Not that this isn't a good solution, and one that I heartily endorse. However, another answer might be: scope out the cities' taverns. The dissolute, in need of money, unpleasant, and dangerous hang out in taverns just as do all other members of the non-noble social strata. While I am really not in any position right now to do serious tavern research, I'm going to go out on a very tenuous historical limb and say that they are, in the 10th Age at least, equivalent to the classical Agora (confusing perhaps, since Milean cities and some cities in the East retain that open public sphere so taverns AND the Public Spaces can serve as cultural meeting points).
If there is a natural habitat for adventurers (outside of the ruin, the dungeon, and the goblin cave) it must assuredly be the tavern. They have no real place in civic public space outside of the Milean law courts. They belong to the dark interior of the burgeoning service industry or to the dangerous wild roads. The inn is an urban campfire around which adventurers may gather.