Myself and 3 friends did Hadrians Cycleway , Ravenglass to South Shields , over 3 days a few years back. It's probably one of the easiest coast to coast routes, not too much climbing and generally very quiet roads. We booked a hotel in Whitehaven for the 1st and last night, after confirming it would be ok to leave a car in their car park and that they had secure cycle accommodation.
Day 1 was a train ride to Ravenglass , then mostly cycle paths to Allenby before diverting inlaid to Wigton, overnighting at the Wheyrigg Hotel ( again secure cycle storage). Day 2 was a longer day, riding very quiet roads along the Solway coast, a busier but straightforward section through Carlisle then quiet roads to Brampton. The route ( very well signposted) then heads up to Gilsland, tracking the wall. We made a mistake here, deviating from the official route we carried on the B6318 to our 2nd overnight stop at the lovely Twice Brewed Inn, in Once Brewed. The B6318 is a very fast road undulating road - I wouldn't use it again! There is an option of a YH at Once Brewed but we fancied the inn! Bikes were locked in a steel container in the car park.
Final day started with a long but gradual climb before lots of country lanes and cycle paths to the outskirts of Newcastle and the riverside cycle path. This being a summer Sunday was reasonably busy with other cyclists and peds, but still very enjoyable. We crossed the Tyne at the Millennium Bridge to take the mostly cycle paths through Gateshead and Jarrow to finish at the Roman Arbeia Fort in time for a look around before our transport back to Whitehaven.
We already knew that a train return that day was not possible due to 'bus replacement' engineering works so had booked transport through
Pedal Power,
https://pedal-power.co.uk/transport/
Bikes were loaded into the back of their minibus and we had a relaxing journey back to Whitehaven. certainly not the cheapest way to finish our ride but cheaper than an additional overnight in South Shields. I think it was about £50 a head for the 4 .
Pedal Power offer this service and lots of others such as accommodation booking, luggage transfer etc. Highly recommended based on that one experience.