Thermal vents among the trees on the hillsides let off jets of hot steam from underground caverns.

BBC: A return to Middle-earth

One answer is to use the energy to compress air, which can be squirrelled away in hermetically sealed underground caverns.

ECONOMIST: Compressed air might help to make wind power more reliable

This involves compressing air and storing it in large repositories, such as underground salt caverns.

ECONOMIST: Energy storage

The energy firm said it would continue to store waste on site until a deep geological disposal facility was made available - similar to the storages created in underground rock caverns in Finland.

BBC: Sizewell B nuclear power station

Kitsch roars its dinosaury head at Grand Canyon Caverns, luring you 21 stories underground for an ubercool cavern tour and even an overnight stay.

BBC: Arizona��s top five scenic drives

M. has basked in the fame of nearby Carlsbad Caverns National Park, with its awesome underground stalactites and stalagmites.

FORBES: How Carlsbad got WIPPed

But as these visions are developed, their potential to become a reality will depend on the success of facilities such as the Jurong Caverns -- considered by Tan as a prototype for underground developments in Singapore.

CNN: Why Singapore is putting its oil back into the ground