There’s a new system called Timewalking, in which people get scaled down to the proper level of the past expansion and can run content. Not all content is available and the only raid of the mentioned expansions is Firelands. Since you have a level 86 character, you can join as well. Starting this Wednesday, the Cataclysm Firelands will be active for a week.
You can join on your priest if you like, we’re going on Tuesday 