During one of your first Mayan adventures with James Kidd in "Assassin's Creed 4: Black Flag", you will learn Edward Kenway's Eagle Vision can double a treasure hunting guide to help you unlock a special suit.
Locating all 16 Mayan Stelaes will unlock the Mayan Outfit in Tulum, worn by the First Civilization, which helps you deflect bullets from your enemies. This will help you a great deal in addition to your other Kenway upgrades.
Each Stelae comes in a form of a puzzle. You have to climb a Mayan sculpture and perch yourself at the top. Once you do so, shapes and lines will appear and you will have to rotate them until you solve the puzzle.
The Mayan Stelaes are hidden all over the Caribbean, so here's are the coordinate locations of all 16 of them, courtesy of IGN.
STELAE LOCATIONS (COORDINATES)
--MAYAN STELAE 1: CAT ISLAND (734, 694)
--MAYAN STELAE 2: GREAT INAGUA (845, 468)
--MAYAN STELAE 3: MISTERIOSA (303, 199)
--MAYAN STELAE 4: MISTERIOSA (296, 196)
--MAYAN STELAE 5: SANTANILLAS (217, 245)
--MAYAN STELAE 6: SANTANILLAS (221, 242)
--MAYAN STELAE 7: TULUM (70, 405)
--MAYAN STELAE 8: CAPE BONAVISTA (179, 593)
--MAYAN STELAE 9: MATANZAS (343, 642)
--MAYAN STELAE 10: TORTUGA (875, 379)
--MAYAN STELAE 11: PINOS ISLE (334, 476)
--MAYAN STELAE 12: PINOS ISLE (342, 478)
--MAYAN STELAE 13: NEW BONE (431, 116)
--MAYAN STELAE 14: ISLA PROVIDENCIA (502, 44)
--MAYAN STELAE 15: ISLA PROVIDENCIA (502, 44)
--MAYAN STELAE 16: LONG BAY (525, 253)
Once you've located all 16 of the Mayan Stelaes, head back to Tulum. There will be a marker on your map that says "Mayan Outfit." Go to the marked area and a scene will commence once you unlock the door. Along with the Mayan Outfit, you will also unlock the Vault Raider trophy / achievement.
