Sewers of Velz

The sewers of Velz are a big maze where all the sewage of Velz flows through. Its built for small creatures only so bigger creatures will have to crawl through most of the tunnels that lead to different sections of the sewers were the actualy sewage comes from homes and other buildings in different grouped. (Basically regions have been grouped to have all that regions toilet, bath and sink water go to 1 specific section in the sewers via magical portals.) Each sewer section consist of a larger circle area where there are 7 portals the spit out sewage into the main stream and main tunnel that take the waste out of the city.
These sewer systems houses a bunch of mosters that the goblins that mostly work there have to deal with on a daily basis, some of these monsters are slimes, rats, shambling mounds, gelatinous cube, Otyugh, Troglodytes, Carrion crawlers etc.
Deep within the sewers lies the door to Dr. Hiller lair which is locked requiring a combination of symbols which can be found within the sewers as well as a key in the form of a special pocket watch. (the puzzle is taken from the Golden claw puzzle in skyrim) The combination of symbols can be found in the sewer in the bigger areas where the ceiling will have one of 4 symbols engraved on it. Which one comes first is determined by how many sewage portals there are, since the rooms with symbols have 1-4 portals instead of the normal 7. The options at the door are as follows - cat, snake, goblin, angel, bugbear, dragon and human The combination is as follow , 1 portal=angel, 2 portals=cat, 3 portals=dragon