1TB Disk filling up

[CommitConfirmed]

My 1TB disk is at 88% utilization. However, looking at the entire /opt/unetlab folder, it's only 1/3 of that. I cannot figure out where the rest of the file system is being used by:

root@training:/opt/unetlab# du -sh
291G

I chased the other 60%+ to /var/lib:

root@training:/var/lib# du -sh
610G

But have no idea what I could clean-up from here?

Any thoughts?

[CommitConfirmed]

Found additional info. I kept drilling down in that /var/lib folder and found that they bulk of the disk space utilization was in the docker folder, specifically:

/var/lib/docker/overlay2

I then found a specific container listed that says its 599G

I'm trying to use the command "docker image prune" to delete this. If not, I'm wondering if I should delete and reinstall docker??