Quoting kenata, reply 27
What I think would be interesting would be to make all three wonders require being built in the same level 5 city, and then adding some mechanic where after the first one is finished the city in question becomes visible to every other faction. Otherwise, a faction could simply rush through the civic tech tree, build all 3 buildings without anyone knowing where or how to stop you. As for the same city req, this would be necessary to stop a player from simply starting all three buildings in three different cities concurrently.
I think the balance should come mostly from researching of 3-4 techs on different trees that give nothing except access to the victory buildings.
Not only that, but to access them you will also require to research most of the trees (all of them, not just the civilization tree), that's certainly balanced with the time and effort it takes to achieve the other victories.
I agree it should be built on a city size 5, but I don't think it should be more expensive than other "wonders", or placed in the same city.
This is more or less the equivalent to the space victory in CIV games.
Considering these 'Wonders' would be victory conditions, I find it completely logical to make them take longer than standard wonders, as well as needing to be in the same city, for a couple reasons.
First, assuming the idea that the city becomes visible to everyone is implemented, it makes it possible for everyone to gang up on you to stop you from producing the structures. The problem is, with the time it takes to cross the map at present, if you have it take 'Normal Wonder Time,' they'll never even get close before you finish the wonders, particularly if you're able to build all three concurrently in your first 3 Level 5 Cities, unless they're already in the process of conquering you of course. This remains true even if they ignore every other city you own, and even more true if you have a city grown out across a choke point. It makes consolidating forces in that choke and cutting your losses to defend that one city far too easy otherwise.
And since we're assuming that you'll have a large portion of all the tech trees explored, since it would be necessary for this victory, in order for any other realm to stop you, they'd have to be ahead of you in at least 2 of the 4 trees. (I'm not even counting Diplomacy for this, since it does nothing to help you stop someone from winning this kind of a victory.) Those trees would almost certainly have to be Magic and Warfare as well, since the other ones would be moot towards stopping said player in any regard other than resource production. But, if you're going for this victory, it's likely you're doing it because you're already sure you have a rather large lead on your opponents in Research Production, making the idea of anyone being ahead of you somewhat laughable, despite you having to spread your research across multiple trees while they only need 1 or 2. The extra time it would take to produce three double or triple-cost wonders in a single city would both help the opposition to close the tech gap, as well as give them time to actually use said tech against you, while still hopefully allowing them time to cross the map to even get to you.
Conceptually, it's a sound idea to keep the wonder creation time similar, and allow them to be separate, but logistically speaking, it's imbalanced heavily in favor of the person building the wonders, since they don't have to set up supply trains to deal with anything. Their supply trains are already set up, and they only have to defend a small group of cities. Even if each wonder took 40 turns, like I said, this means they need 3 Level 5 Cities capable of producing the wonder, a Choke-Point, and Time. It's basically a guaranteed win if you don't drag the time scope out to near-epic proportions.
