I do not understand the meaning of de wa, I thought it meant something like at the / in the (location) - But in this sentence, I don't know. hmmm
In addition to marking the place where an action happens, で (de) has another meaning. It marks the means by which something is done e.g. バスで = (go) by bus, はしで = (eat) with/by means of chop sticks.
In this case it is marking how the seeing is done. 一人で (hitori de) = by means of one person, i.e. by oneself.
The は (wa) is separate from で. This is the usual topic marking particle. In this case it is acting in its contrastive role. The contrast here is that by himself he could never see the view, but with the implication that he could see the view with the help of others.
By the way this is not a full sentence. It does not say "It is a view that ...". It is simply "A view that ...".