The Hall of Radiance is the name applied to the largest room of the Iceberg Cavern, which is located in Endless Ocean: Blue World's Weddell Sea. It is a room notable for its spires of ice, as well as the multitude of crystalline formations that cling to the walls. There is a section of this room that is above-water, but nothing particularly of note can be seen if the player surfaces. The only way in and out of this room is the tunnel in the floor of the Hall.
In order to gain access to the Hall of Radiance, the player must first enter Lower Ice Cave 3 from the main area of the Weddell Sea. After doing so, they will pass through the Crystal Globe, an area named for its beautiful ice structures resembling gemstones, and then go through a twisting tunnel, emerging in the Hall. The first time the player has to go into the Crystal Globe, the way into the Hall will be blocked by large spikes of ice, which the player must break with the help of the Leopard Seal that lives in the dome (the sound of the Sea Whistle causes the seal to charge at the player, and when the player dodges the Leopard Seal rams into the ice blocking the way instead, breaking it).
The creatures that live inside of the Hall include Antarctic Silverfish and a small group of Leopard Seals (including the legendary individual named Leo), as well as the occasional Bald Notothen (which are found only under zoom-mode patches). However, during the main storyline, the player will also encounter a Spectacled Porpoise (a species that is not otherwise found inside of the Hall) with a white patch on its fin that has been separated from its pod. Its cries of distress sounded so eerie and ethereal echoing through the caves that the player and their troupe believed that it might have been the Song of Dragons. However, upon discovering the Porpoise and discovering that it is the true source of the mysterious cries, the player will be tasked to heal the distressed creature with the Pulsar, and it will subsequently become one of the player's diving partners in thanks.