I ended up combining this with a favourite memory from when I lived in Lisbon a while ago - the fluorescent jellyfish in the Oceanarium (Europe's largest indoor aquarium!).
I've been working on incorporating the feeling of bare feet in soft sand, the visual (jellyfish dancing in the dark), the blue-black ocean surrounds and then a sound bite... I originally had the idea to use waves (that we hear from outside) and underwater (that 'they' hear beneath the surface), but then I thought about the dance - and I woke up to the sound of Strauss' 'The Blue Danube' in my head. It was perfect - especially since the jellyfish keep in time ;)
It's quite an abstract space and rather dark in there for my basic camera to do it justice, but here is a pic and you can view the vid below.