I like Fortifications. Well, Fortification. There's only one. I like the idea of building things onto lands. I've dabbled with them in the past, but this I think is the cleanest design I've ever done for one.
It does a thing when the land is tapped, like the original. It's a gold mine that makes Gold tokens. Doesn't cost a lot, but it's a lot of early investment just on this if you want to Turn 1 this card. It's why I costed it that way. You can Turn 1 land, play this, Turn 2 land, tap both to fortify a land, then on turn 3 you can use it when you tap the land. Very very slow for most constructed formats. Limited might like it, as it makes any-colour mana sources. Sometimes being slow is worth it for mana-fixing, if you're being greedy. Slow mana fixing in limited? Common.