>>719872958
You can get to Shellwood right from the begining of the game. Near the elevator just to the west of the Marrow fast travel station there is a jumping section far above Bone Bottom village that requires you to have dash or float, but you can cross if you pogo off of flies. After crossing that path there is a simple door. If you use the simple key to open the simple door you enter the wormways. The wormways are fairly linear so as long as you keep going up you will come out even further above Bone Bottom and it will lead you directly into Shellwood. All you need is 500 Rosary, and the spot right near the elevator has a nice little loop of rosary dropping enemies that can give you 500 in about ten minutes.