Hello, Mrs Hg137 here.
We found this trackable while walking the Thames path, between Oxford and Abingdon.
This is a nice, simple idea – there is a chain, on which are to be threaded bottle tops, added as the trackable progresses on its way. There was just one bottle top on the chain when we found it (or maybe it had become full?), but more kept appearing on the chain as we kept it for a short while.
Oh my, I had loads of fun with this trackable! Great idea!