It is virtually impossible to find a good detailed rail map of an area that shows all the lines and stations, that you can use for planning. The so-called rail maps on most websites are laughable, only show a few main lines and giving no useful information to show where lines do and do not go, and which places have stations. Click here for one of the better examples, but which still only shows about 50% of the main lines and no stations. Google maps is even worse, you have to zoom a long way before it will show you rail lines, and it is impossible to get an overview.
I think I have found one: http://www.öpnvkarte.de/
This shows rail lines, métros and buses. The coverage is best for Germany (it is a German site), and the further from Germany the more gaps in the coverage. But, it gives a good overview of where you can get to and by which route.
Note this URL contains the letter 'ö', which in some countries may not be on your computer keyboard. I advise you to either click on the link above, or copy-paste.