Akkala Ancient Tech Lab
Located in the far northeastern corner of the map. Robbie, the eccentric scientist, will offer to sell you Ancient Weapons and Armor in exchange for Ancient materials and Rupees.
Before he can do this, you must relight the furnace outside his lab with Blue Flame, just like you did in Hateno Village. The blue flame source is located down the hill, across a dangerous field full of Moblins.
Robbie runs the lab with his wife Jerrin, and the crafting machine he calls "Cherry" (a nickname for his first love that still annoys her) opens for business once the furnace is lit. Trade Cherry Rupees — from 90 for a single Ancient Arrow and 1,000 for each weapon or the shield up to 2,000 for each armor piece — plus ancient screws, shafts, springs, gears and cores salvaged from Guardians, and she will forge Ancient Arrows, an Ancient Short Sword, an Ancient Shield, an Ancient Bladesaw, an Ancient Spear and Bow, and the three-piece Ancient Soldier armor set. That armor already resists ancient and Guardian weapons; upgrade it to two stars or higher at a Great Fairy Fountain and it starts boosting the damage those same weapons deal instead.
From the Ground Up
After buying a house in Hateno Village, Hudson will travel to the Akkala region to start his own town. You will find him on a circular island in Lake Akkala.
He will ask you to bring him massive amounts of Wood, and to recruit people from all over Hyrule whose names end in "-son" to work in his new town. This is the best side quest in the game and unlocks Tarrey Town, a massive hub with unique merchants.
Every request for Wood is really a request for a new resident. Greyson, a Goron recruited from the South Mine near Death Mountain, clears the boulders blocking construction; Rhondson, a Gerudo tailor found at Kara Kara Bazaar, opens the town's clothing shop; and Fyson, a Rito trader pulled from Rito Village, sets up a general store selling arrows. The last resident needed is a priest — Kapson, recruited from Zora's Domain — because the quest ends with Hudson's wedding to Rhondson in the finished town, with Kapson officiating. Complete it and Hudson hands over 3 Diamonds, and Granté, Robbie and Jerrin's own son, turns up on a rooftop selling rare armor and a one-time replacement for a broken Hylian Shield.