The final act largely takes place outside Nirn, offering a complete change of scenery while resolving the crisis threatening the world. The stakes are at their highest: the heroes carry on their shoulders the fate of all Nirn. This act combines exploration of an extraterrestrial location, final puzzle resolution, and confrontation with the main enemy.
Act IV – The Star Bastion (Finale)
Synopsis
Arrival on the Moon
The PCs set foot on unknown terrain. If they go to Masser, they discover a sterile surface of ashen dust, carved with craters, under a sky where Nirn appears as a gigantic bluish ball on the horizon – a striking spectacle. Quickly, they can find the entrance to an ancient structure beneath the lunar surface (as indicated by Dwemer plans or divine guidance received). This structure could be an ancient observatory of the Ancients or a Temple of Masser left by Merethic mages. Exploring this place offers strange scenes: low gravity (jumps are higher – beware of Athletics, but also risks of slower falls), corridors lit by an unknown luminescence, inscriptions in lost languages. References to the refugee colony mentioned in fan-lore can be integrated: for example, finding traces of an ancient Khajiit colonization attempt on Secunda or Masser (frescoes showing Khajiit caravans climbing towards the sky, a nod to Temple Zero myths, or even encountering the ghost of a Khajiit on the moon who tells the story of their people who lived here briefly).
Final Trial – the Celestial Pylon
At the heart of the lunar complex lies the sought-after artifact – let's say an Aetherius Pylon, a kind of giant crystal or a mechanism connected to the stars. It is the weapon or tool that can shut down Numidium or counter the Thalmor's spell. But of course, the enemy has not left them undisturbed: the final boss or its emissaries await them there.
Campaign Note
Final Confrontation
If the main antagonist is a Thalmor Archmage who orchestrated the entire plan, they too could have traveled (by portal or twin vessel) here to prevent the PCs from sabotaging their ascent. The confrontation then takes place in the Pylon room – an epic duel mixing unleashed magic and melee combat amidst cosmic rays. Alternatively, Numidium itself can project part of its essence or send Daedric avatars. The PCs could face a giant Dwemer animoncule or a Dremora Lord as the ultimate obstacle. Another memorable option is the arrival of an unexpected ally: why not the legendary Nerevarine in person, piloting the giant golem Akulakhan (Morrowind's unfinished second Numidium) as in Kirkbride's writings. He fights the main Numidium in space around Nirn to slow it down while the PCs activate the Pylon – a strong nod to fan-lore, to be reserved if your players appreciate these crazy references.
Resolution: Activation or Failure
The characters, if they defeat the boss, finally have the opportunity to interact with the celestial Pylon. Here, a moral decision or a crucial choice can be introduced: for example, the artifact can be used in two different ways. Either destroy it to trigger an energy wave that instantly deactivates Numidium but risks shaking the laws of Mundus (close to the Landfall scenario where Nirn is destroyed – perhaps not entirely but it could cause cataclysms). Or reconfigure it to divert Numidium's energy towards the moons, saving Nirn but transforming Masser into a kind of new, dangerous Land of the Gods.
Campaign Note
Heroic Success (Nirn Saved)
If the PCs manage to neutralize Numidium without annihilating Nirn, the war below ends abruptly. The orichalcum colossus collapses and the Aldmeri fleet is defeated. The heroes return to Nirn in triumph (aboard the vessel if it is intact, or via a portal created by the artifact) acclaimed as the saviors of the world. This epilogue allows for a positive conclusion: Imperial ceremonies, bards' songs recounting their legendary journey beyond the moons, restoration of peace… and eventually the beginning of new challenges (for example, what to do with the acquired knowledge of planar travel? leave this technology in the hands of the Empire, destroy it, or use it to explore even further in future campaigns).
Campaign Note
Landfall (Nirn in Ruins, Adventure Continues Elsewhere)
If things go wrong – by choice or by failure within the allotted time – Nirn suffers the full brunt of Numidium's wrath. This is the Landfall scenario where the world as we know it is ravaged. The PCs, meanwhile, find themselves stranded on the moon or in space, having to survive in exile with any other refugees. They see Nirn's surface ignite from the moon. The campaign does not necessarily end there: it takes on a post-apocalyptic survival turn on Masser or Secunda. The characters could decide to found a colony (as described in futuristic lore) and search for other survivors in the Mundus system. A "sequel" to the campaign could then consist of exploring the moon's caverns (where unknown creatures or the remains of a Daedric base might reside) and preparing a possible return to Nirn generations later to rebuild it. It is a bitter, but epic and open ending that respects the vision of some fan writings on the world's destiny.
Conclusion
Whatever happens, the campaign will have offered players an unforgettable adventure, blending free exploration, mysterious dungeons, political conspiracies, pitched battles, and stellar odyssey. The major themes of lore will have been addressed: the Empire/Dominion rivalry, Dwemer vestiges, the Thalmor's excessive ambition, the intervention of the gods (perhaps Akatosh or Lorkhan himself subtly manifests during the end), and the possibility for mortals to defy the impossible.
This solid foundation allows for new scenarios if desired. For example, if Nirn has survived, the heroes could be sent as diplomatic emissaries to other continents (Akavir, Atmora) taking advantage of their new aetherial transport. If they are stranded on the moon, the Masser colony offers a whole new long-term role-playing framework (resource management, magical terraforming, internal conflicts between refugees of different cultures, etc.).