What if we had a look out job, or border patrol duty to single dwarves or squads were the dwarf or dwarves leave the fortress for some time and then comes back with info about the surroundings of your fortress. You could have maps (accessed from some menu or something) where you could "load" the sites adjacent to your fortress, but instead of loading everything you would load only what's visible from the point of view of a dwarf entering from a point either in the surface of the cavern layer.
So, if you dwarf is travelling the surface and there are no cavern entrances then you would only be able to see the surface level.
Other side of this would be that depending on the skills/memory of the dwarf the descriptions/maps could differ more or less from the reality (details like trees and such could be randomly generated with increased randomness for poor memory/observation skills dwarves). Also depending on their skills (like tracking and others) they could potentially spot sieges before happening and in the case of squads even engage(and hopefully defeat) small raiding parties or other small enemy groups.
If they are given mounts they could do this rather faster than dwarves on foot. They could also escort caravans if the need arises and in general be the first ring of defence of your fortress.
And so on.
Obviously this would have to wait till the army arc but I don't know if such thing as explorers/patrolling/recon was contemplated.