On higher difficulties the opponent AI does a good job of building walls to avoid culture flips on cities that are close to yours.

If you decide to pursue culture victory and there are enemy cities close by that you know you could easily culture flip in the next several turns, make sure to send a spy into the nearby town to see if they are building a wall. If they are you can have your spy stop production of the wall which gives you that many more turns to potentially culture flip it.

Walls stop flips on Rev?

Walls stop flips on Rev?

Yes, Until someone build the Wonder "Hollywood".

I guess they took the idea from the wall that DDR built to prevent the west cultureflipping East Berlin.