There's probably a thread on this already, but which train station is most beautiful/noteworthy?

I like Grand Central, Gare du Nord, Milan's main station, and Hamburg's.

Also, is any FTer old enough to remember the old Pennsylvania Station in New York?

My personal favorite is the wonderfully restored Washington D.C. Union station - what all great train stations should look like. Amtrak had similar plans for L.A. and Chicago, but I think they ran out of money?

The grand old stations you mention are built to such a scale that the traveller has to look from a good distance to grasp their architectural merit. Given their respective neighborhoods, I doubt the average train rider takes the time to notice them

Some of the features which make a memorable station, in my eyes:
- it has to be a dead-end station, not a through station
- vast single overhead area for all trains are preferred
- flagship trains leaving for major destinations; I do like the mix of high-end trains from Europe's many railways at stations such as Milano.

Not to say the above features are the most functional.

I'll give a special mention to Buenos Aires majestic but desolate station (mostly local trains these days), and another to the well-executed, very modern Kyoto central station.

Nothing too special here in Switzerland.

The Gare d'Orsay isn't shabby, though it seems to no longer be used for trains. Among the other depots (love that word) in that city, can't say I've ever noticed anything about the Nord, but I love looking at St Lazare and trying to imagine what Monet saw.