I used the Extract command on Rhythmbox; it took an appropriate amount of time for each of 21 tracks, with a status message near the bottom of the UI indicating that it was extracting 1, 2, etc. But now I cannot find the music, nor documentation on where Rhythmbox Extract puts the music.

In case it matters: I extracted to MP3, I have lame installed.

EDIT: Yes, I have looked through the folders in ~/Music/

EDIT 2: I have even done a search starting at / for words I think should be in extracted filenames, but didn't find anything that way either. However, the output of that is large, I was hoping someone could tell me where they're supposed to end up.

You set up your your Rhythmbox "Music Library" in its Preferences. Click on the hamburger menu icon ≡ and then select Preferences. once you are in the Rhythmbox Preferences Window, select the Music tab on the top:

Under Library Location you can change the field Music files are placed in: to your choice. The default is the Music folder within your "Home" (AKA /home/$USER/Music).

You can also change the Library Structure here, but the defaults work fine for me.

You may want to change the Default Format from Ogg Vorbis to MPEG Layer 3 Audio (in other words, mp3) and the next field from Ubuntu to Variable Bit Rate or something like that.

finally at the very bottom click on the Install Additional Software Required button to install the mp3 codec.

Where in the Music Folder?

You may find your music from the CD under the folder /home/$USER/Music/Unknown/Unknown and the music files named:

01-Track 1
02-Track 2
etc

If Rhythombox cannot figure the Artist/Album names, etc.

Hope this helps