An underwater cave in Mermaid Bay, where Alex and Conner meet the Seafoam Spirit for the first time in The Wishing Spell. They are able to breathe there because they are sitting inside a large air bubble in a big clam shell.
"There were coral pillars in the cave with dark, rocky walls behind them. A sandy floor was underneath them, and they were facing an endless blue ocean."
They are escorted back to land by mermaids.
- ↑ TLOS I, ch 18, p. 339