It looks like the inspection pit is being re-built.

Peter Kerslake says "Situated just to the north of Merthyr Tydfil Dowlais Cae Harris was one of the three small sub sheds of Merthyr, with this view from September of 1956 showing its 5672 at rest as work is in progress on the inspection pit.
Designed for sevice in locations such as this within the Welsh valleys the two hundred strong class had been built as two batches of one hundred each from 1924 and 1927, with no less than 87 of the initial 100 being based at Welsh depots in the mid 'fifties.
Mr. Collett had continued in his design with the use of inside cylinders and a 0-6-2 wheel arrangement from the pre-grouping classes earlier inherited by the G.W.R., his class proving immensely popular with the Welsh footplatemen, his "Taffy Tanks" being equally at home on both branch line passenger services and freight duties.
First inroads were made to the class from 1962 but 5605 was the last to survive in traffic until 1966, with nine making it into the preservation era."