Maybe you could find the last dwemer colony below blackreach,but I was thinking what if they kept digging and awakened some sort of long hidden enemy then Tamriel might have a new danger to face,this could link in to the mining complex idea because they are still digging down but they might have had to barricade some entrances to keep the newly awoken hybrid-like enemies at bay. The forge idea is good,maybe the dwemer could have built the forge? Core of Nirn? no,they would have to dig miles down to reach that The Chaurus hive is a good idea ,maybe the "Uruk-hai" sort of creatures I was refering to could be some sort of Falmer/Chaurus hybrid but were in-cased in rock-like pods,but were awoken by the dwemer digging? Firelands,no wouldn't really see that fitting in unless they wen't all the way down to the core.
