Mystery

I've been trying to get the chimney swept for months, so far unsuccessfully. Early this morning a text from the sweep - can we pop round in 45 minutes? They arrived on time, did the job, no fuss, no mess, and were gone again within 30 minutes, leaving us with the all-important 'Certificate of Chimney Sweeping' for the next occupants of the flat.

Despite good intentions, it was only a very short walk this afternoon. Passed this structure on the way. It's in a garden by a footpath, and we often wonder what it is. Rumour has it that it's an observatory, but who knows?