Green Glass Doors

In Green Glass Doors, players take turns suggesting something that can go through the Green Glass Doors, and only those who know the secret rule can answer correctly every time.

The object of the game is to figure out the secret rule by observing what can go through the Green Glass Doors, and by asking about new things.

What determines whether something can go through the Green Glass Doors has to do with the content of the thing being suggested or asked about.

If something is spelled with double letters, it can go through the Green Glass Doors.

Considerations

One thing to consider when playing Green Glass Doors is whether all the words in a phrase or description have to have double letters for that thing to pass through, or whether any word in the phrase having double letters is good enough. For example:

Can Cookie Monster go through the Green Glass Doors, even though a Monster can’t?

My recommendation is to require all words in a phrase to have double letters to go through the doors, since the title of the game has so elegantly managed to include double letters in all 3. If you want to play a version of the game where double letters in one of the words is good enough, check out the other games that share the rule.