Known as the Yorkshire Dales Explorer, the return service has been running between Rochdale and Ribblehead twice a day on Saturdays, since June 8.
It calls at stations including Manchester Victoria, Salford Crescent, Bolton, Blackburn, Clitheroe, Hellifield and Settle.
More than 1,000 passengers have travelled north of Clitheroe on the service since it launched and almost a quarter (24%) of them have gone on guided walks run by groups like Lancashire Rail Ramblers.
Craig Ward, chairman the group, said: “The service has been quite popular. Some passengers just come for the ride as it’s such a scenic route. Others come for a walk and we’ve had a few cyclists as well.
“There have been groups of walkers from Manchester who had never travelled to the Yorkshire Dales by train before. Historically, they went to the Peak District because they couldn’t access the Dales on a direct service.
“But this gives them the chance to travel there without using their car, meet like-minded people and explore the Dales.
“There’s a different atmosphere on board because everyone is going for an enjoyable day out. People talk to each other and the regulars get to know each other.”
Lancashire Rail Ramblers have also organised coach trips, from Ribblehead to Swaledale and Wensleydale, for passengers who want to get off the train and travel further afield.
Lizzie Bushby, deputy chair of the Yorkshire Dales National Park Authority and member champion for recreation management, said: “We welcome this new service which appears to be already proving popular.
“The national park is there for everyone to enjoy, an amazing green space in which to relax or to exercise, and the benefits to mental and physical health of doing so is proven.
“We also know the service has been enjoyed by residents of the national park travelling the other way. We sincerely hope the service continues and look forward to welcoming everyone off the train and into this iconic landscape.”
Northern offers adults £25 return tickets from Manchester Victoria to Ribblehead, so ramblers and nature lovers can enjoy an affordable day out in the Dales. Railcard discounts are also available.
They can make the journey between those two stations in around two hours, travelling along a route which features some impressive scenery.
Trains depart from Rochdale at 7.52am and 2.52pm on Saturdays, calling at 18 stops before they reach Ribblehead. The return trains depart from Ribblehead at 11.08am and 6.05pm.
Customers alighting at Ribblehead can take a short walk to see the famous Ribblehead Viaduct or catch another train to continue north on the Settle-Carlisle line and visit other destinations in the Dales, such as Garsdale and Dent.
Northern is the second largest train operator in the UK, with 2,500 services a day to more than 500 stations across the North of England.