what is your favourite game within another game?

[Stardom22]

Sometimes you can be enjoying playing games played on PC and realise that some of them are just embedded within other games. For example the Fallout New Vegas and the caravan, The Witcher 3 and the Gwent
among others.
What about you?

 

[eLdavis]

None so far, I think the closest I have had with this is racing within GTA San Andreas.