To farm Weathered Crisis Fragments efficiently in Path of Exile 2, follow these key strategies and routes centered around Citadel farming on the endgame Atlas:

Run Tier 15 Stone Citadel Maps: Weathered Crisis Fragments drop specifically from the boss Doryani in Stone Citadels, which appear on Tier 15 maps in mountainous, coastal, or Vaal City biomes. Ensure your character or group can handle tough Tier 15 boss fights.

Maximize Waystone Drop Chance:

Use Waystones heavily crafted with suffix modifiers, ideally a 6-suffix corrupted Waystone, as only suffixes increase the drop chance of Crisis Fragments.

Corrupting Waystones with a Vaal Orb can convert all mods to suffixes, dramatically boosting fragment drop rates.

Aim for at least 300% Waystone Drop Chance to commonly get 2 fragments per boss kill; increasing above 900% can yield 3 or even 4 fragments.

Use Atlas passive skills that enhance Waystone Modifier Effect and Drop Chance to further boost fragment yield.

Employ Precursor Tablets to increase the number of Waystones found on maps, indirectly improving fragment farming efficiency.

Optimal Atlas Passive Setup: Temporarily respec your Atlas passive tree to focus on Waystone-related nodes to maximize Waystone drop chance and effect while farming Citadels. Once done, revert to your regular farming setup.

Fast Clear Builds and Pathing: Use clear speed optimized builds to run as many Citadel maps as possible per hour. Efficient Atlas pathing to find Stone Citadels quickly also increases your farming rate.

Be Prepared for Increased Difficulty: 6-suffix corrupted Waystones make maps significantly harder, so only run these if your build is strong or farm with a capable group.

Trading and Alternative Sources: While farming is primary, you can also acquire Weathered Crisis Fragments by trading with the Currency Exchange NPC after reaching Cruel difficulty if you need smaller amounts.

These methods combined maximize your drop rate of Weathered Crisis Fragments from Stone Citadel bosses, speeding your progress in obtaining all Pinnacle Keys and unlocking the Burning Monolith boss fight.