i can'T find incan city

[Dungeon of sea]

i got the map of a lost incan city but its north west of gran granada. but when ı am going there there isa only trees. i can't find where it is. and also a second quesiton hot can ı attack all big cities. ı can only attcak poor settlements. and what is the purpous of sneak into town. what is my object in sneak to town