I love the idea of this game! This sounds like a great way to rediscover the city that you live in. Here are my ideas for some cards.

Title: Nature Detective
Description: Take 5 minutes to find some hidden pieces of nature in your surroundings.

My idea with this card is to get the players to see that even though they are in an urban environment, nature is still around them. Even if it's just a glimpse of the sky between buildings, some insects on the ground, weeds popping up between cracks in the concrete, or a squirrels in a park, we sometimes forget that nature is all around us even when we are in an urban setting.

Title: Fake History
Description: Find an interesting building, landmark, or area and create a fake history of what happened there.

Even though we may not know the history of the city we are in, we take take a guess at what it used to be like. You can be as realistic or dramatic as you want. It can be fun to make up stories about the world around us.

Title: Go Against the Grain
Description: Walk in the opposite direction of the majority.

Sometimes you just need to go where everyone isn't going. You may find empty streets, old abandoned buildings, or quiet places away from the hustle and bustle of urban life.