The North Wales Coast railway line will be closed for major engineering work between Chester and Holyhead (including the branches to Llandudno and Blaenau Ffestiniog) for the entire month of January-
Rail Replacement buses will be in place to all stations.
So of note for anyone going to Holyhead for the ferries to Ireland, or to Conwy.
Having said that I have been on RRB's non stop from Chester to Holyhead and the service is faster than the train, due to the A55 expressway.
https://www.leaderlive.co.uk/news/26182498.north-wales-coast-line-close-entirely-four-weeks/