Lots and lots and lots of guilds.
You are right in the sense that Horde RP is often more fantasy-based and diverse, just due to the nature of the faction!
When it comes to guilds themselves, the Valley of Honor is a hub for a variety of guild types- Mercenary, Military, Crime, etc.
However, lots of guilds on Horde are not based near the cities and are easily discovered through the discord that Itlaris posted above!
Of course I am obliged to mention the PCU, a big ol’ collection of guilds that have a strong presence on the Horde side. If you are looking to take part in epic-scaled rp campaigns and events with loads of players from both Alliance and Horde,- the PCU is a good place to be. The guilds in the PCU are all dedicated to creating RP and uniting roleplayers in order to create huge epic stories for us to enjoy!!!
Most of the PCU gamer gang can be located somewhere on this thread guild-wise, I’m sure there will be something for you!