In an 1844 edition of the Columbia Spy, Edgar Allen Poe wrote, “When you visit Gotham, you should ride out Fifth Avenue, as far as the distributing reservoir, near Forty-third Street, I believe. The prospect from the walk around the reservoir is particularly beautiful. You can see, from this elevation, the north reservoir at Yorkville; the whole city to the Battery; and a large portion of the harbor, and long reaches of the Hudson and East Rivers." He's talking about the Croton Reservoir, of course, where the New York Public Library now stands. (In fact, you can still see some remains of it there.)
That elevation Poe referred to was from the promenade, which hosted groups of gatherers on a daily basis, making for a "delightful scene at night, with the moonlight dancing on the water." Forgotten-NY points out that there was even a Croton Cottage, at 5th Avenue and 40th Street, which stood from 1845 to 1863 and provided refreshments for visitors (it burned down during the NYC Draft Riots). The city also designated a potter's field to the west of the reservoir as a public park, called Reservoir Square.
The reservoir, a massive tank holding water from the Croton River, boasted walls 50-feet tall and 25-feet wide. It was completed in 1842—a moment historian Henry Collins Brown called "the greatest forward stride in the city's history, [with] the general introduction of running water." (Prior to that, think rain buckets.) By the 1890s it was being torn down since it was no-longer-needed... and by 1902 the cornerstone was laid for the New York Public Library's main branch.