Ninja Taro

This can only be done after the events that take place in Ogre Castle late in the game. When you're done entirely with that area, return to the house of Kondo's daughter, which is just one screen west of Omi Village's outside area. Speak with Kondo's daughter to get an unlimited supply of ladders!

Normally, throughout the course of the game, you will be forced to only obtain one Water Spider from the Geko Castle area, with the rest of them (as many dungeons require multiple Water Spiders) being dropped on rare occasions by enemies. There is a way to make sure your supply, however, is unlimited, greatly making your journey easier.

When you discover the secret in the Wind Scroll, head to Geko Castle and into the southeastern well's cave. Soon, you will come to an area (the seventh screen total) where there is a backwards-"L" protrusion from the northern wall. Go north from this screen to the next. (The spikes you see blocking the way are some you can walk on, at least the westernmost two sets.) In the next area, go northwest and use a Water Spider to cross the river there. Then go east from the treasure chest you find and navigate through the spikes as you did with the entrance to this area (some are fake). Cross the river again when next possible, then cross the river one more time when that path ends. Go north and west from there, past some more fake spikes, to the staircase.

This will lead to an otherwise-inaccessible passage in the ninja master's house. Go south from where you appear and you will go through the wall. Speak with him and he will allow you to have an unlimited supply of Water Spiders!

Note that this trick can only be executed when you obtain the consumable version (i.e. the one you actually use) of the Offering item. Head to the unnamed village you first visited near the very start of the game, then go one screen east of there. In the southern portion of that area is a mushroom statue - use the Offering on that statue to create a bridge. That bridge will take you to a portion of the area where an enemy will continually reappear upon its death and will almost always drop heart-emblazoned pickups, which are used to boost your defense and thus lessen the damage you take.