Mt. Ember

Mt. Ember can be traversed as soon as the player has arrived in the Sevii Islands, provided the required HMs have been taught. After Surfing north of the Ember Spa, a Move Tutor will offer to teach Explosion to a compatible Pokémon. A pair of Team Rocket Grunts are apparently standing guard nearby, talking in loud, easily overheard whispers.

Further up the hill, Rock Smash and Strength allow access to a network of caves which lead to the Legendary bird, Moltres. After the National Pokédex has been obtained and the player speaks with Celio, the Team Rocket Grunts will challenge the player to a battle. If victorious, they will flee, allowing access to another chasm, inside of which lies the Ruby required by Celio to enable trading with Hoenn. It is found in a room with a Braille inscription; the previous room gives a letter-by-letter translation aid. By continuing along the pathway (only one way until B3F where the path splits), the player will find that the cave is in fact circular, and they will be back at the entrance.

Along with the Dotted Hole, this is one of only two locations in the Sevii Islands that has Braille writing, located both in the room with the Ruby and the room directly before it.

Mt. Ember in the anime

Mt. Ember (referred to as Mt. Magma in the dub) appeared in The Search for the Legend. Upon arriving on One Island aboard a ferry, Ritchie met a man named Silver, who was headed for the volcano, prompting Ritchie to follow him. While traveling together, Ritchie learned that Silver had once seen Moltres, one of the Legendary bird Pokémon, and had decided find and battle it one day.

Eventually, they found Moltres, but found out that it was weak. Butch and Cassidy, attempting to use Moltres's weakened state for their advantage, tried to capture it, but their plan was thwarted by Ritchie and Silver. After Moltres regained its strength from the volcano's magma, Silver started battling it using his Salamence. The battle was, however, interrupted when the volcano started to erupt, forcing Ritchie and Silver to retreat. Despite the interruption, Silver still intended to finish the battle one day.