The Bottom

Mine level 120. Take the lift five levels at a time, and go on days you can commit: food, a decent sword, and bombs from level 40 onward speed things up enormously. The lower third (purple slimes, shadow brutes) is where deaths happen, so keep your health topped up. Reaching the bottom earns the Skull Key for the Desert's Skull Cavern - and much later the same mines get a harder remix in 818922349.