Magic Bean

In Ocarina of Time, these magical beans can be purchased from a man sitting near the Zora's River who seems to be constantly eating. They can be used by planting them in mounds of soft soil which are located all over Hyrule. Give it seven years or so and they should turn into platforms which will grant you access to certain areas you couldn't reach before.

These also make an appearance in Majora's Mask, but this time around they only take a bottle of water for them to fully grow.

Tips
Even though planting Magic Beans in soil will help gain access to different areas, Link shouldn't place them straight away. First, he should bottle some Bugs and drop them into the soil first. This will result in a Gold Skulltula jumping out.