To unlock this achievement, you'll need to complete 9 challenge tombs from the base game. The earliest time you can unlock it is after you have returned from the 'Mission of San Juan' region.
No special gear is needed, you can complete them as soon as you have access to the region. Some parts of the map are locked initially and you'll need to advance the story to get access. I listed the tombs in order they get available.
To reveal tomb locations, talk to the locals, or watch the video under the spoiler tag.
For the video, all credit goes to
PowerPyx
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The guide follows this format:
Areax.
Tomb name Skill reward name - Skill description
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Peruvian Jungle1.
Underworld Gate Caiman’s Heart – Health regenerates more quickly.
2.
Judge’s Gaze Eagle’s Perch – Increase climbing skills to traverse the environment with more speed.
Kuwaq Yaku3.
Howling Caves Huracan’s Mantle – Reduce damage from fire and explosions.
The Hidden City4.
Temple of the Sun Hoatzin’s Hunger – Increase the amount of natural crafting resources gathered from each source.
Cenote5.
San Cordoba Caiman’s Breath II – Further increase breath capacity when swimming underwater.
The Hidden City6.
Ancient Aqueduct Jaguar’s Paw – Increase chance to knock enemies down with melee attacks.
Mission of San Juan7.
Tree of Life Kinich Ahau’s Boon- Health is instantly restored once, when near death in battle. Refreshes between encounters.
8.
Thirsty Gods Sip’s Strike – Charged arrows deal more damage against armored enemies.
The Hidden City9.
Path of Battle Sip’s Quiver – Loose up to three arrows without pulling from the quiver.