The Smallest Chapel in the British Isles

It's the Costello Memorial Chapel at 16 feet long by 12 feet wide.

 The Costello Memorial Chapel was erected by Edward Costello to mark his devotion to his wife, who died in 1877 at the age of 46. Mr Costello had been a substantial farmer at Dromore a few miles from Carrick, but had moved to the town during the early part of the 1800’s and set himself up in business. He was widely known as a man of great kindness and charity and was partly instrumental in bringing the Marist order of nuns to the town. 

On the death of his wife, Mary Josephine, he had work on the memorial Chapel started. It was to be both a monument to his love and a last resting place for his wife and himself. The little building was dedicated on April 22, 1879 and after the consecration ceremony, the body of Mrs Costello was placed in a sunken space to the left of the entrance, and covered over with a thick slab of specially made glass. The body, which was interred in a metal coffin, had been embalmed when Mrs Costello died, and had been cared for in the interim by the Marist nuns. Mr Costello himself died in March 1891, and his remains also in a metal coffin were placed in a sunken space to the right of the entrance. A thick glass lid was placed over this vault too, and today the inscriptions on both coffins can be read with the aid of a torch. Mass was celebrated in the chapel on every first Friday from the time of its consecration to Mr Costello’s death, but no religious service has taken place in it since.

More here.   And when you get there, do click on the link to photographs.