General considerations of ownership & access
The land on which these railways used to run will now come under different types of ownership - certainly very few will have been made into a public right of way. In some places the land still belongs to the railway. Some sections will have passed into private ownership where there is no practical restriction to walkers. In other places walkers will not be welcome. In practice land where you are unwelcome is often the most uninviting, land which has been ploughed and no longer looks like a railway line. It does no one any good to walk the trail where the trail has been erased.
In any event this guide is not offering any recommendation in specific situations. Cases vary. In Ireland there is no real tradition of public footpaths, people have tended to walk where they will, at their own risk, across farmland and wild land. This situation has changed in some cases because of the pernicious practice of pursuing ridiculous negligence claims against landowners for accidents. The fear of possible litigation has prompted some landowners to post 'keep out' notices.
Speaking of accidents there is a real problem with bridges and tunnels. Once the railway has gone no-one is prepared to maintain these. As a result you may find some tricky or even dangerous obstacles. The same can be said for bramble, gorse and thorns on almost any stretch of the line, not to mention of course a great deal of water and mud!
Maps, equipment, transport to areas...
The best maps available are the recent Discovery series 1:50000 OS maps, which are the only maps to show disused railways and to have adequate detail for getting around rural Ireland on foot. Publication is not yet complete but most of the west is well covered. Northern Ireland is covered by the same survey, although the maps are coloured and presented very differently.
Wear stout waterproof boots to cope with a rough and wet surface and strong clothing to deal with the undergrowth. Expect the weather to change from beautiful to miserable and back, on almost any day of the year.
You should bring some supplies. Away from villages and towns shops and pubs can be very thin on the ground. The good news here is that these shops are generally open at all hours, or will open for you.
Most of these routes connect with the existing railways at one end but even so modern rail services are patchy in some parts. Some notes on access are given for each of the routes