The Cartographer's Toolkit is a legendary crafting material used by the Blacksmith Haedrig Aemon to craft the Board Walkers Boots.
The Cartographer's Toolkit drops from two sources in Sanctuary: Lavarinth and Enkidu. Both elite mobs are Ghoul creatures.
It has a chance to be dropped by Lavarinth in Rakkis Crossing (Act III). Lavarinth spawns during the "Blaze of Glory" Event which is triggered by talking to Captain Haile.
Another source the Cartographer's Toolkit may drop from is: Enkidu. He spawns during the "Eternal War" Event in Festering Woods (Act I). In contrast with the previous source, this one is a random event.
While exploring the Festering Woods, keep an eye to the mini-map constantly. You will see a yellow dot on the mini-map pointing at an event.
Note: You are not looking at the monument atop the hill (That is for the Last Stand of the Ancients Event).
What you are looking for is a square on the ground which triggers the Eternal War event.
Board Walkers - Boots
This recipe requires a few materials you don't usually acquire by disenchanting: Ascended Greaves and Cartographer's Tool Kit.
The Ascended Greaves (Boots) is a random loot obtained mostly from clicking on decaying armor, angel corpse, and loose stone throughout the Battlefield of Eternity (Act V) in Pandemonium.
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