Since most of the comments (and TFA) is about solitude, but more in nature, I want to chime in about solitude in an urban setting. For the 18 months I was a digital nomad (while waiting for a US visa to move back near my cofounders), About 6 months were spent in cities where I didn't know anyone when I arrived, and roughly about 3 months were spent in "city solitude", the first couple weeks in each new city I went to.
During this time I wouldn't really have any directed conversation with humans. I'd thank a store clerk, make an order at a cafe or restaurant, that's it. Mostly because I didn't know the local languages in some of these countries (Asia), but sometimes even where I did. I was incredibly lonely the first time it happened due to the former (language), but towards the end of my nomadism it meant something else. I began to seek that time, and use it to commune with the place, the city, and to think truly independently without disrupting my lifestyle. These are big bustling people-filled places I'm talking about -- Seoul, Tokyo, Taipei, Osaka, Bangkok. I can speak Japanese fluently, yet every other week I spent in Tokyo I'd avoid personal interactions, while still going out regularly for dinner, or a run, or to a cafe. You start to see the place as a friend, and understand it more.
Ironically, you begin to be able to understand humans better from this time not being a part of their society. It's stepping away from individuals (friends/family/coworkers/date) you focus on, and suddenly you can observe the humanity around you with an even emphasis. You can see which things they take for granted, how they prioritize life, what makes them tick. You see things, learn things, understand the guiding fabric of their society (and to some extent the global one) from a third-person perspective, which is very different from what I saw while an active part of it.
This same perspective also makes you feel a great deal of freedom from those social rules, yet acute awareness of them (much like with a friend, you don't have to deal with their lifestyle if you don't want to, you can look at their life more objectively than if they were your partner or family). You think about things, try things, plan things, make choices very differently than if you are being socially influenced directly by those around you. Being a foreigner/outsider in those places probably accentuated it, but likely is a prerequisite to feel that way in a city.
I really feel like it permanently changed the way I see the role of society, places, and my human relationships to be a completely different perspective.