For me;
1. Forge, means you a head start to battles. (if you wanna use it 7/24 you should have 6 city in forge island and use theocracy)
2. Poseidon, it's cut in half travel time.
3. Colossus, can be really usefull when you stuck in battle.
I think these are most usefull temples. But also hades is deserve to be mentioned of course.
For me;
1. Forge, means you a head start to battles. (if you wanna use it 7/24 you should have 6 city in forge island and use theocracy)
2. Poseidon, it's cut in half travel time.
3. Colossus, can be really usefull when you stuck in battle.I think these are most usefull temples. But also hades is deserve to be mentioned of course.
Hello!
It depends on how many cities you have..
But Hades' Grotto is a godsend if you are in the conflict zone.
It returns a percentage depending on its level of the cost of creating resources of all units destroyed during battles in your own cities, they are returned as marble units.
In a naval battle you collect somewhere around 40.000-60,000 marbles/round
In a land battle you collect somewhere around 70.000-150.000 marbles/round.
The amount also varies depending on what type of units are in the battle.
But you can easily make 2,000,000 marbles.
It is active for 16h.
The cooldown varies depending on their number, their level, and the chosen form of government, just like with other wonders.
I have 15 cities on islands with the following wonders:
The next city will also be on the grotto... obviously 
I am attaching a screenshot.
As a complement, since I can no longer edit the post..
I ask a moderator to edit it for me. Thanks in advance.
Either you win the fight, or you put a vacation, or you convert it, or you move it. Otherwise your opponents will rob you.
They never took anything from me.
Frustrating for them. 
