In addition to pedestrianized spaces (or I guess technically as a subset of them, since you usually can't drive cars into these either) another kind of urban space I enjoy is the transit station. Let me tell you why!
1. Vaulting Architecture
While I suppose one could go to a big box store or a warehouse to experience wide open spaces that are also indoors, transit stations (specifically, usually, train stations) manage this with a completely different, far superior vibe.
Let's start with Chicago Union Station: these skylights make the room feel more open, more expansive, and more impressive all at once. The typical vaulted/arched ceiling gives the place a feel of lightness and airiness despite being absolutely clear that we are indoors thank you very much.
Amsterdam Centraal gives us an arched feeling too, though here we are out by the tracks, so the space is deliberately ambiguous about being indoors or out--it connects to both the clearly-inside market halls and the clearly-outside train line north. Here the sense of enclosure matters as much as the sense of openness; it straddles the line in a way that makes my heart happy to see it.
Haarlem Centraal does something similar, but note that which part of the station is actually open has changed: the archway is not open, but the side gratings are. It's appropriate to a station that is more open than Amsterdam Centraal was but still wants to give that overarching sense of space.
2. Public Monuments
A really good station (as opposed to just a stop) gives an opportunity for more public art and public interest than just a pretty roof.
Public art outside a train station (here in Paris, I believe at Gare du Nord) gives a sense of significance and willing occupation of space. This station is not apologizing for its street presence, like some metro stations do, but boldly claiming that it is a meaningful spot in the city, and that you ought to look at it.
Even smaller stations, like Aquarium T station in Boston, can have a sense of street presence. The tilted glass box here isn't as flashy or noticeable as the big flying bear in Paris, but it still says that this is an interesting, different spot from all the plain office buildings around--or the Aquarium itself.
And it's not station-specific, but it would be an utter failure not to mention Chicago's Loop, the champion of not apologizing for its impact on the streetscene (and since the Loop has so many stations on it, you could almost call it a single giant station with internal transit).
A good station is a public monument, a space that draws attention not only for use reasons but because the city wants you to know it is there, and it matters.
3. Somewhere To Sit
A good station isn't just pretty; it's also functional. And that means that a good transit station has seating, as well as food, bathrooms, and other amenities.
Sadly. this is less photogenic, so I tend to photograph it less, but you can see that in addition to large areas for people to pass seated customers (which is also important!) Haarlem Centraal has seats.
I didn't take pictures of seating in Amsterdam Centraal, but you can see the whole concourse here of amenities: things to do while you wait for a train or after you arrive on one.
And while it's not the focus of this shot of the TGV in Gare du Nord, you can see the seating on the empty platform as well.
My struggle to find pictures of this is really a function of the fact that I use it--so unless I take more selfies, I don't tend to have pictures of the seating, even though it's really important!
So to sum up: a good transit station has a sense of openness and wonder; a clear artistic sensibility that is willing to take up public space; and practical elements that make it pleasant to exist in it.
I think this WMATA station in DC does a great job of all three, so that's probably a good point to end on. Look at that architecture! I'm glad the Metro comes frequently, but I could still appreciate spending time in such a space.
