1,1'-Bi(cyclohexyl)-1,1'-diol (two cyclohexane rings joined by a bond between the two carbons that each carry an OH group) is treated with acid. The rearrangement product is

One OH is lost to give a tertiary cation on one ring carbon. A ring C-C bond of the neighbouring carbinol ring migrates to it, expanding that ring from six to seven members and leaving the carbonyl in the large ring. The spiro carbon is then the original cationic carbon, so the product is spiro[5.6]dodecan-7-one.