The Shinjuku Historical Museum 新宿歴史博物館 has a database of over 500 images of (mostly) postwar, pre-1970s Shinjuku. See their website for photos.

I stumbled upon a series of photos from circa 1952-1955. Here are two version I stitched together. The left side of the photos shows the east exit of Shinjuku Station; beyond the station is the Yamanote Line tracks and, in the far background, mountains.

Here is the first panorama:

Here’s the same panorama, merged using a slightly different method:

One of the first photos in this merged image can be found here, labelled:

These photos were taken from approximately this location: Google maps

Among the landmarks visible in this photos is the old Kinokuniya Bookstore 「紀伊國屋書店」:

See also:

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