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, there is another use for the soil. Link should bottle some Bugs and drop them into the soil. This will result in a Gold Skulltula jumping out. This can be done even after a bean is planted.

Here are the locations of soil Link can plant magic beans in Ocarina of Time:
 * 1) Right next to the magic bean salesman.
 * 2) In the Lost Woods, in the area with the bridge connecting Kokiri Forest and Hyrule Field.
 * 3) Again in the Lost Woods, near the area with the Forest Stage.
 * 4) In Kokiri Forest near the shop.
 * 5) Right next to the warp platform in the Death Mountain crater.
 * 6) At the bottom of Gerudo Valley on the small cliff next to the cow.
 * 7) Outside the Lakeside Laboratory in Lake Hylia.
 * 8) Next to the entrance to Dodongo Cavern
 * 9) Next to the entrance of the Spirit Temple
 * 10) In the Kakariko Graveyard