As Kagen said, anyone can see them once you can see Dungeons. Click on Actions, then on Dungeons.
Demi said:
Then you see:
Right here it says "normal" "heroic"
Did you mean you could see the words "normal" and "heroic"? If so, that's what you need. Click on the word "heroic." They're little buttons. The default is normal, so the normal dungeons are displayed. If you click on the word heroic, it displays the heroic dungeons. Kagen listed the 10 different army units that are needed for various heroic dungeons. (I've been trying to train one of each as I researched as I went along. GENDY gave me advance warning about the needed units for heroic dungeons so I wouldn't have to dismiss a high level army unit to train a sandrunner when I finally was able to run them. That would suck.)
I just sent my army into a dungeon or I'd post a screenshot for you.