>>715798539underground passage is dark with a bunch of enemies (including fast dogs, hidden enemies, and arrow spam) the fastest way is down main street with the dragon. If you just wait out his breath attack its an easy run, you just have 3 sections you have to do that in the level.
Alternately, the dragon is easy to kill with bow cheese from the first tower, you just only hit him once or twice per his attack (that you are above and immune). Buy lots of arrows and hunker down but it goes an item worth a good chunk of souls and it gone forever.