"This is a big railway station."

Translation: Ez egy nagy pályaudvar.

[AntalAron]

Vasútállomás?

[vvsey]

Could be that, too.

[Dave81791]

Ez nagy pályaudvar. Was accepted as ok, even without 'egy'. Is it correct?

[dcseain]

egy is often optional in this construction, so yes, without should be valid i think.

[Richard401939]

Railway station : what is the difference between a pályaudvar and a vonat állomás ?

[Imre565437]

We don't say vonatállomás, but vasútállomás. The pályaudvar is bigger than the vasútállomás. There are many rails in a pályaudvar, whereas a vasútállomás may has only one rail.