An authentic North Wales Quarry locomotive, 0-4-0ST Lilla was built by Hunslet in 1891, works number 554, for the Cilgwyn Slate Quarry where she worked a lengthy rubbish disposal line in conjunction with Manning Wardle Jubilee 1897. She is of a unique design, although dimensionally very similar to Cackler, now at Thursford as a static exhibit and Jerry M , now working at Hollycombe both former Dinorwic Quarry ‘Mills’ class locomotives.

By 1928 she was surplus to requirements at Cilgwyn and sold to the Penrhyn Slate Quarry. On arrival at Penrhyn she was given a major overhaul during the course of which she acquired the rather crude but authentic patches to her tank, and lost her crosshead feed pump. Although a relatively large locomotive, there is no record of her ever having been used on the main line. She was used within the quarry until about 1954, at which time she was put into store and was for several years part of the melancholy line of surplus locomotives dumped at Coed-y-Parc.

In 1963 she became the first of the Penrhyn locomotives to be bought privately when she was acquired for preservation by the late Bernard Latham, who finally completed her restoration to working condition in 1972.  She travelled around several locations, including Kew Bridge, Knebworth Park, and Bala Lake.

It was from Bala Lake that in 1993 she came to the FfR as a participant in the Hunslet Hundred Gala, and having no home to return to, remained at Boston Lodge. In 1997 the locomotive was offered for sale, and was subsequently purchased by the Ffestiniog Railway Company, the purchase price being underwritten by the Lilla Locomotive Group.

There is no evidence of her ever having been reboilered by her previous owners, so when the boiler, by now 113 years old, was showing definite signs of distress at the end of the 2004 season, the decision was taken to purchase a new boiler and at the same time to carry out a major overhaul and a new boiler, effectively a welded replica of the original, was fabricated at Boston Lodge.

Lilla is helpful on the FR, providing "drive-an-engine" experience runs, "Slate Shunts" and Corporate Training days, usually in Minffordd Yard, with some of the FR's vast wagon stock on which Lilla always looks at home.

She is to visit the L&B as the guest engine for the September 2011 Gala.