I wanted a block to do single leg calf raises so I made this.
Can be used for calf raises, calf stretching, elevated heel squats, or self-defense.  ;P
Make sure to use it on a yoga mat, gym flooring mats or at least a carpet so it does slip (safety hazard warning).
I used the fuzzy skin to help make it a little grippy for use with sneakers. 
It's printed its side so the top can get the fuzzy skin applied. If placed upright the skin “fuzziness” will noy apply to the top.
I set it with 6 walls and placed a modifier to add a solid infill wall in the center for added structural support.

If you use PLA you can reduce print time by almost 4 hours if you change the “Max Volumetric speed” from 12 to 25. 
But only PLA! I cannot say what will happen with other filament types!
Since this is just a basic shape/object the quality is not really affected by the faster speed. It worked for me and saved me 4 hours'ish. 
If you do change it, make sure to set it back to 12 so your other prints are not affected!