One of the main ways adventuring can be achieved is through the archives that appear in the larger cities. In these archives, you can browse the local book collection to gather various maps and charts in the field of your choice. Browsing a field costs 500 per look, you can browse through the archives approximately 40 times before you become mentally tired. Once you become mentally tired you must visit another city before you are able to use the archives again or you can use head ache medicine
You will gain one of the following effects when you browse through a field: you write down clues you have gathered to form a map to a potential discovery, you gain one to three skill points in that field, or absolutely nothing happens. The most common occurrence are the skill ups. The only maps you can gather from browsing the archive are ones you actually have the skill to discover, which means, the higher your skills are, the more likely it is you'll find a map while browsing.
You can also not have two of the same map at once, although once the discovery on the map is made, you can get it from the archive and discover it once more, you can even report it again! In addition, if you have discovered a map, but not reported it, you will not get the map. This can be used to target a specific map by discoverying but not reporting maps you don't want. This increases the chance of getting the map you want without filling up inventory slots with maps.
You can get multiples of the same map by giving a map to a friend and browsing again. This is often a method of leveling skills by doing the same high level map over and over again.
If for some reason you lose a map from your inventory you can get it again by browsing again.
Maps sorted by category
There are six different fields that can be researched in the archives: Geography, Archaeology, Theology, Biology, Appraisal, and Art. Each of these fields have their own specific discoveries or maps to various kinds of treasure. Here is a collected list of the various maps and what they find, whether it be a discovery or treasure (especially useful when you see someone selling a map and you want to know whether it is worth your while or not):
Maps sorted by location.
Most of this info comes from the Japanese wiki. This list is by no means complete. Any help with the missing pieces would be appreciated.