There is an excellent collection of duel maps here:
/topic/at/2317/
I've added a few more!

Guardians (author – Berlov, St. Petersburg). In my opinion, this is the best map ever created. The cities of rivals are located next to each other; only azure dragons separate the passage (and an event that resets resources upon passing through). And then – freedom of creation; on this map, you can do anything, and there is no single path to victory. Although the map may initially seem poor in resources, there are more than enough; you just need to know how to fight for them. The map has no weak points; the only thing is that with good play from your opponents, the game can be long. The quests are not annoying; everything fits organically. It’s an asymmetrical map; each race has its own development path. Those who haven’t played or seen this map will find it difficult to explain what happens on it. Those who have played and didn’t like it might find that custom maps aren’t their forte?
But still, try playing as a barbarian, a demon, or a beastman. Try rushing your opponent red across the upper sea in 2 weeks, break through the azure dragons with gorgons and vampires, collect at least cursed armor, admiral's hat, and legion figurine, visit all the islands, free the prisoners, complete the quests – maybe you will change your mind. This map is the only multiplayer map that is interesting to play in single-player mode.