Which main city buildings make QI encounters easier? There are several but none of them are easy to come by. While they all provide substantial military boosts for various settings, I’ll only describe the QI special boosts here. Note, where you can manage more than one of each building type, their boosts do stack.

Forgotten Temple – a temporary building lasting 28 days. While active it gives both red and blue QI troops a 50% boost for attack and defence. However, it’s only available as a GE level 5 reward. Being able to finish GE level 5 each week does have it’s rewards …

Tourney Grounds – a temporary building that last for only 14 days. While active it gives both red and blue QI troops a 25% boost for attack and defence. However it requires 500 fragments from GBG encounters and we win only 1 fragment on maybe 20% of those wins so it takes a lot of fights. If you have a Royal Tower of Champions – it provides 3 fragments per day.

Yggdrasil – a permanent building but needs to be level 9 for a QI benefit.
While active at level 9 it gives only red QI troops a 50% attack boost. You win this as the main prize for completing the Viking Settlement.

Shinto Temple – a permanent building but needs to be level 9 for a QI benefit. While active at level 9 it gives only blue QI troops a 20% defence and 40% attack boost. You win this as the main prize for completing the Japan Settlement.

Royal Bathhouse – a permanent building but needs to be level 6 for a QI benefit. While active at level 6 it gives only red QI troops a 20% attack and 20% defence boost. It also gives blue QI troops a 60% attack and a 20% defence boost You win this as the main prize for completing the Egypt Settlement.

Sun Temple – a permanent building but needs to be level 9 for a QI benefit. While active at level 9 it gives only red QI troops a 50% defence boost. You win this as the main prize for completing the Aztec Settlement.

Mughal Temple – a permanent building but needs to be level 6 for a QI benefit. While active at level 6 it gives only blue QI troops a 60% defence boost You win this as the main prize for completing the Mughal Settlement.

Hut of the Sacred Instruments – permanent building needs level 9 for QI benefit. While active at level 9 it gives only red QI troops a 30% attack boost You win this as the main prize for completing the Polynesian Settlement.

Information provided by Radical69, Shadows in the Night Guild Member