While playing on hard mode I require alot of footmen and people to fight in general. Due to the large group of fighters I have it makes it difficult for them to advance in level. I thought it would be cool to have a place that they could battle one another and gain XP. This could also provide as entertainment for the Hearthlings to increase morale. Plus it would add something cool for people to create and experiment with different group tactics and mixture of units.
In the middle of my town it would look so dope to have a little Colosseum. Maybe add a traveling merchant that will have creatures in cages that I could release into the arena. This way while playing in peaceful mode there can still be the element of combat.