How do you stop an ice grotto melting?
Every year an ice grotto is carved into one of the largest glaciers in Switzerland.
It has been attracting tourists since the 1870s, but recent temperatures in Switzerland have been some of the warmest on record and the Rhone Glacier is shrinking.
In the last five years, the glacier has retreated by about 150m (492ft).
Some worry the grotto could be having an impact on the melting of the glacier, but an ingenious trick is being used to protect the ice above the tunnel.
The BBC Travel Show's Jo Whalley went to find out more.