Tower of Time

Most likely you will receive it automatically as you progress through the game. The easiest way to get it is by killing the Orc Leader on Hard or Epic difficulty for the Fair Fight trophy. Just try to gather your fighters together and place a Healing Totem on them, by the middle of the battle you will easily heal 1,000 health points. I recommend using the right branch of totems for this, since they last longer, and in the later stages of the game, with maximum leveling of your skills and heroes, you can install a new totem as soon as the old one runs out.