It's a cottage, although they might perhaps be conducive to people "indoor camping". It's pretty much at the shore (past the Narrows and turn left), so it'd be handy to the pubs and the like.

Aha - found it online. It sleeps 4-6:
Anchor Cottage                
3 Steel Dickson Avenue
Portaferry
County Down
BT22 1LE                
Telephone:        (01273) 304638
http://www.ards-council.gov.uk/accomodation.htm

MUDCAT TAKES OVER ENTIRE STREET:
Oooh, I've just found another TWO on the same street:

Inisharoan Cottage NITB approved 3 Star rating ***
7 Steele Dickson Avenue,
Portaferry,
BT22 1LE
Owners: Colin & Elma Hagan, 16 Shore Road Portaferry, BT22 1JY
Tel: 028 4272 8512
http://www.portaferry.freeserve.co.uk/Self-Catering.html

and Camomile (terrace cottage - sleeps 4)
9 Steel Dickson Avenue
Portaferry, Co Down
Northern Ireland BT22 1LG
Telephone: +44 - 012477 - 28541
http://www.travel-ireland.com/accomni/selfdwn.htm