On this page of the game guide to Borderlands 2 you will find a detailed description of the side mission titled To Grandmother's House We Go. You can begin this quest in the Eridium Blight location during the completion of the main mission named Toil and Trouble.
1) Bounty Board
Take on the mission  at the Board. The road to the house is marked with dots on the map. After getting there, collect five Flowers on your way to  to receive additional experience points.
Reaching the house  will result in being attacked by a group of Bandits. Kill all the enemies and enter the building (though the entrance on the other side). Inside the room you will find only a Goliath. Get rid of him and pick up Grandma's Buzz Axe from the bed. Return to the Board  to collect your prize.