The «Spiral Cliff» is level 24. You have to progress to the top of the cliff facing waves of enemies. The level is pretty short and the achievement is not too hard with some practice.
I did this with my level 33 frost mage. I have all the health increase skill points and 2/2 speed skill points.
I went back to the first shop: «Villager’s shop», at the start of the map. I bought the wand/staff to the right, with +10% speed increase (330 gold).
I ran past all enemies and did not use any skills. You may need some practice to avoid taking damage and know where the enemies are or where they spawn. At the end of the level there is a lot of enemies, just run through them to end the level.