I didn't know where else to put it, but the Treasure Trail Map that requires you to go into West Ardy, Tip.It says you needed to have start Plague City. Correction: You need to have completed Biohazard. The mud patch/sewer path is only available at the beginning of Plague City, after you complete the quest, you can't do it anymore. The only way after that is by completing Biohazard. I didn't really know any way to show proof of this... But I guess I can show that you can't do the mud patch. :S