I think Yogananda is right about the power of being surrounded by nature. At the same time, I have to thank John C. Lilly for inventing the isolation tank. For I strongly attest that supremental realization can occur through extended floatation, even in city settings. Because I did it in a multi-floor apartment complex in Yonkers, NY in 2015.

also, I just came out of a beautiful guided meditation based around compassion at the Thubten Ling (FPMT-associated) Buddhist meditation center in urban Deerfield Beach, FL.

So, isolating yourself in nature is certainly an approach. But definitely not the only approach.