Pingos in Norfolk

I am often bemused by image requests that land in my email from various stock agencies that I have work with but this one had me stumped! The nearest my brain could get to it was Pingu, that very humourous and multi-lingual (all of them gibberish) cartoon character. Thank goodness for the Internet and Wikipedia, which soon sorted out what I was looking for. For a change Fate was smiling on me because I am just off to Norfolk and have added pingos to my shooting list but will need to pack my walking boots, and maybe resuscitation equipment because the specification is for 'collapsed pingos'. Still don't know what one is - well look it up, it isn't what I expected!