Something just came to me now as I was reading these responses; perhaps it's already been hypothesized, I don't recall, but solution 9 could come from the Eighth Umbral calamity timeline's future. Perhaps they created an entire city and had it travel back in time to long before the timeline split (or created the city after they arrived) in order to escape the Ninth Umbral Calamity. Chrono Cross event in our future? It's probably something way more mundane, but it's fun to think about.