Hey, see at the end of the second series, is the giant building in the background of the last shot a prison? It'd make sense to go to a prison afterall, I mean, preestablished fortifications, abundace of weaponry, easily quarantinable sections, hallways and rooms, space for a smallholding..the only problem would be the resident prisoners-those still trapped in their cells, those that escaped but are using the prison as a centre for various criminal activities and those that have turned into zombies/walkers.
Plus-why did the samurai sword woman have a couple of pet walkers?