If you haven't already used Live SQL then you're missing out. This free (Enterprise Edition) database instance provided by Oracle as a sandpit for trying things out and learning new stuff is a great resource. More importantly, it tends to be kept in line with the latest "hot off the press" database release.
So it came as no real surprise last week when it was upgraded to the latest 18c version (which is really just 18.104.22.168, however is now on Oracle's new Calendar Year naming convention. I know I'm a bit late here, however I've only just got around to writing this post. :)
Oracle Database 18c Enterprise Edition Release 22.214.171.124.0 - Production
Check out the new features (Polymorphic table functions, private temporary tables etc) - various Oracle guys have already uploaded a bunch of sample scripts to get you started.