Here are some I found by internet search engine:
Otters Geo, Shetland
An interesting geo, presumably a cave which has collapsed relatively recently, and still with a very narrow entrance where the original cliff face still stands. It hardly looks like otter habitat though.
www.geograph.org.uk
Otters Cave, Moray
Otters Cave, Moray - local area information, map, walks and more
getoutside.ordnancesurvey.co.uk
Sloc a'Gharaidh Ghil, Iona
The "Otter's Cave" - only accessible at low tide.
www.geograph.org.uk
Otter's Cave, also Iona
Also, are you interested in parts of words (cotter, plotter, rotter)?? e.g. NC1 has
Cotterdale House Cave
Cotter End Pots
etc.
Would be interested to know what the project is