Goron City

Once there, walk the tightrope right across to the lone Goron sitting on a
platform. Talk to him to hear about his brother, Darunia, then walk back
across to the ledges by the entrance. Go down the stairs all the way to the
bottom level and step on the mat in front of the closed door. Take out your
Ocarina and play Zelda's Lullaby. Then, when the door opens, stand on the mat
in front of Darunia and play Saria's Song to make him dance! After he's done
dancing, he'll give you the Goron's Bracelet, which lets you pick up the Bomb
Flowers. Now, leave Goron City.

Back outside, find the area where there's a Goron sitting by a group of Bomb
Flowers. Then, pick up a Bomb Flower and throw it over the edge at the cavern
far below. If you threw well, you'll destroy the boulder, granting you access
to Dodongo's Cavern! Go back down the mountain and enter the cave.