El Nido is a dilapidated yellow homestead surrounded by multiple drawers, barricades, and barrels. Large vines crawl up the walls of the house, and the water fountain has been left untreated. Inside the building are numerous boxes of dynamite.
El Nido was built on Guarma many years ago. Some point prior to 1899, it became an outpost for rebels loyal to Hercule Fontaine.
Events of Red Dead Redemption 2
After Hercule Fontaine saves the Van der Linde gang from the Guarma soldiers, they run into the jungle from the soldiers reinforcements. Hercule brings them to El Nido, where he has hidden a stash of weapons which he proceeds to give to the gang. After successfully repulsing the attack of the soldiers, Hercule and Leon bring the four gang members to the La Capilla region.
El Nido is in fact the farthest notable point of Guarma.
El Nido's name is confirmed in the index files for the in-game map.
As with Manicato, El Nido doesn't become labeled on the map upon discovery. This most likely points to the obvious reason that its probably due to Guarma's incomplete nature, or perhaps it wasn't meant to be.