From Medivia Online Wiki
The Vigilante's Hideout is located north of the City of Abukir through the mountain and deep underground.
Starting from the shovel hole in the Northern desert you can get there following this route: (map does not show the paths that are one-way only)
You will need Key 7007 to unlock the door to enter. There are several daily respawn items found here including some Crossbows, Arrows, Swords and Food.
There is a postbox to the west side of the area provided you have completed the The Postman Missions Quest
Monsters located in this area:
There is 1 Hero, 4 Vigilantes, 4 Tar Monstrosities, and 9 Archers scattered about the Hideout along with a huge number of Wild Warriors and some Hunters too.