CastleMine from Mugshot Games combines tower defense with a little bit of old fashioned digging. Instead of mapping out mazes for creeps to crawl through or building balloon things on green green grass, you get to dig underground one block at a time. Uncover extra gold deposits, additional resources, or even nests of enemies as you attempt to defend your castle from the threat from below.
CastleMine very neatly divides gameplay into two general phases: digging and maintenance. Your first task is to tap a shovel icon to dig through a block of soil. You can only dig sideways or down, not up, so when those shovel icons appear, choose with care, as you're creating the very path your foes can use to attack you. If you dig out blocks of gold or crystal you'll add to your resources pool. If you dig out a relic you'll gain some additional XP. If you hit a skull, enemies become more difficult but you'll be one step closer to a perfect score in that stage.
When you're not digging you'll be placing towers in the dirt or upgrading them once they've gained enough experience. There are nine defense towers ranging from fire balls to lightning, stingers and shock towers. You also have a few support towers that increase adjacent tower abilities, adding another layer of strategy that becomes very important later in the game.
The lure of delicious resources is tough to resist in CastleMine, but you can't just go digging all crazy like if you want to keep your castle safe. That slight tension between gathering gold and keeping defenses strong will keep you glued to this game for a very long time. Later levels get difficult without much notice, and you have to experiment with upgrades vs. new towers, just like most defense games of this nature. But with 150 levels and an entire array of tech trees to fill out, there's no shortage of strategy in this delightfully unique tower defense game!
NOTE: This game was played and reviewed on the iPad 3. Game was available in the North American market at the time of publication, but may not be available in other territories. Please see individual app market pages for purchasing info.