Really, the oldest? Yes fo'real, I too was skeptical upon first hearing such a claim as the aforementioned, alas mateys, it be true. Granada is full of old buildings awash in pleasant pastel tones, smells of good restaurants, and yet the omnipresent epic humidity..
For about 60 Cordobas ($3,US) you can climb to the top of the west tower of the older church pictured below. Well worth it to get another perspective on the streets below.
San Juan del Sur is pretty nice granted, but the real ticket are the beaches the dot the coastline on either side to the north and south, as SJDS itself is pretty hippie-gringoed and access to these other beaches requires a car or hitching a ride, thus such is kept out of their reach and influence and thus the first set of photos isn't from SJDS itself, but of of of these nearby areas; Playa Majagual.
One is able to enjoy these beaches which dot the coast just north and south of SJDS in almost solitude. Another stark contrast is in the two seasons in Nicaragua, those being the above pictures showing the brown of dry season and those below showing the lush verdure of rainy season.
About a 2hr drive from Managua, lots of coffee comes straight outta this region of cloud forests and cooler temperatures. Not many gringos make it up this way either compared to the beachy areas as well, which makes for an even more authentic (feral?) experience.
One is able to enjoy these beaches which dot the coast just north and south of SJDS in almost solitude. Also, the above pictures show the brown of dry season and those below show the verdant green of rainy season.