Intense Gravity Planets

Planets with gravity that is so intense that special armor is required to not be crushed to death on.

 

I would add to this that not only is armor required for survival, but -movement- as well. Plain humanoid legs aren't going to get much ground on a planet with high gravity!

 

or this gravity could affect different races differently because of their structural make up.

 

It would be kind of interesting trying to get over cliffs on a planet like this...
Also, in order for it to be so dense, wouldn't it need to be either really big or have a lot of heavy materials? If that's the case, then it might be worth it to explore these planets to collect those dense (and possibly rare) materials!