Thanks for the chapter!
Hope those two can keep having the city and location a secret. Otherwise a greedy government official is probably going to try to demand he transfer ownership, for a small remittance, that or some powerful noble or small fry will try to threaten him into turning it over to them for self serving lame excuses like they deserve it and he doesn't. In any case, it'll be interesting to see the facilities and state the city is in. Would be interesting if there was a functioning underground transport system.
However, before he can use any of it he'll have to complete the mountains of paperwork and reports that have accumulated over the centuries! If he starts now maybe his great, great, great, great, grandchildren will see a noticeable dent in the pile.