Adam There do appear to be tanks set to the rear of the structure. I would most certainly suggest that this is a vent of some description. Of what, it is unclear. The area i in a depression, in a valley bottom- Has the area been drained? Old pond...? Lanfill site of some description? Is it a capped mine shaft? Need more information really.... Have you checked archive maps of the area...Coal Authority? Regards Andrew Summerton BSc CivEng (Hons) Senior Structural Engineer Direct Dial: +44 (0)1274 534069 email: [log in to unmask] <mailto:[log in to unmask]> <http://www.robinsonconsulting.co.uk/> 1 - 2 Merchant's Quay : Ashley Lane : Shipley : West Yorkshire : BD17 7DB Tel: 01274 532500 Fax: 01274 534000 www.robinsonconsulting.co.uk <http://www.robinsonconsulting.co.uk/> This message is confidential; its contents do not constitute a commitment by Robinson Consulting except where provided for in a written agreement between you and Robinson Consulting. Any unauthorised disclosure, use or dissemination, either whole or partial, is prohibited. If you are not the intended recipient of the message, please notify the sender immediately. ________________________________