Note that AI Dungeon uses GPT-3 under the covers (though by default it's apparently a weaker "Griffin" variant; you can pay to get the stronger "Dragon" model.)

If you don't have access to the OpenAI private beta, you can use AI Dungeon to play around with GPT-3 by starting a custom scenario and pasting in whatever prompts you want; for some ideas see Gwern's excellent post: https://www.gwern.net/GPT-3#the-database-prompt.

I'm particularly impressed with the "database prompt" experiment, which seems to suggest that GPT-3 has some level of self-referential reasoning, as you can tell it what it does and does not know in the context of a session, and it will "act out" an exchange based on that epistemology.