You are correct that you can get by rail to Ostia Antica by rail, but I meant not by Metro, as none of its two lines gets there. Moreover, again a small mistake: you can connect at EUR Magliana but NOT at Magliana, which is on the line to the airport. Of course, neither this is on a real Metro line! Without wanting to start a discussion (especially since the OP et al. had a nice day in the centre), when telling non-residents where to go to and how, we should all be more precise.