Scheme In Common Lisp?

Hello /prog/

I recently got myself SBCL to play with. Now i also want to play with scheme maybe, but instead of downloading a separate program i was wondering if there is a scheme implementation in common lisp and if there is more than one which should i use.

I have the setup file of racket, tough id rather stay with only one lisp interpreter.

I considered the option of writing my own implementation, even if for just educational purposes.
Good idea or bad?