Basically this challenge is the same as the achievement and a great guide has been written up here:
However below I'll include some minor additional information.
I believe you must own the Morrowind expansion to play this, I don't think ESO Plus will grant you free access.
Technically any level character can do this but things will be much easier the higher level you are and the better gear, stats and abilities you have.
The first thing you should do is the Champion of Vivec storyline which will also get you this achievement:
This is pretty standard, go here and do this, come back, repeat. Basic fetch quest stuff.
The one issue you may have is that one boss in one of the later quests you fight may destroy you. You should have got two pieces of armor from Vivec at this point, I would suggest equipping those and then add whatever else you can for health regeneration.
Another part to be aware of is that something will happen in the later quests that will show up in the game world that will destroy the performance of the game, I suggest getting through this quest as soon as possible to return performance of the game to normal. (Although the general performance of this expansion is still shoddy.)
The next thing you can do is also tied to another achievements and that's for finding the tombs.
Great guide can be found here:
Now two things to note.
The rubbings will count as one item in your inventory per rubbings, so maybe this isn't a huge problem but make sure you have the inventory space.
The second thing to note is that I unlocked the Ancestral Tomb Hunter achievement only upon getting the 30 tomb rubbings. The achievement itself says you have to also go to the hidden library which I hadn't done yet. I assume for the Savior of Morrowind achievement/challenge you will have to go to the library and finish the full quest line.
You'll have to kill the six world bosses.
I found this small map here (sorry, bigger one isn't on their site) that shows their locations.
If you're familiar with world bosses, just show up to their spots and then fight them with a group. If you don't have a group, random players should show up relatively quick. If the boss isn't there then you'll have to wait for it to respawn which I think is fairly quick but if you have other bosses to kill then maybe it's best to go do those and come back. That's your call though.
The only boss to make note of I think is Wuyuvs. He'll screw up your vision and you'll get green around the edges of your TV, this is normal and it will pop up and fade multipel times during the battle.
Upon completing the sixth world boss you should see that boss's specific in-game achievement unlock along with "Defender of Morrowind".
On your map you should see a white skull and sword for bosses you have completed and black skull/swords for the ones you haven't.
In order to get credit you don't have to be there for the start of the fight.
Complete Master Explorer.
First you'll have to find the "striking locales" which will be giant eyeballs on your map.
Second part is you have to kill the delve bosses.
The delves all typically have a quest tied to them, so I suggest grabbing those outside their entrance before going in. Once inside, do everything for the quest and then look for the delve boss if you didn't happen to stumble upon them when doing the quest.
Do the Nchuleftingth Group Event.
Do the Forgotten Wastes Group Event.
Both above events can be found using this guide:http://teso.mmorpg-life.com/forgotten-wastes-nchuleftingth-g...
They're pretty much just slightly harder delves. The Nchuleftingth might be the harder to get done of the two if you're a solo player because you have to specifically navigate to this area.
Then the last thing you have to do is complete 32 quests for "Morrowind Grand Adventurer" which you should save for last as some of the above will count towards this total but at any time if you want to check your progress:
-This section is divided into four sections, go to the third one labeled "Quests"
(I had about half the ones I needed after completing everything else.)
All in all this should take you under two days give or take. If you have work or a life, then I suggest working on this a few days before the end time if you want to complete this Challenge. We can't account for server downtime and the game crashed a lot for me while in this expansion.