A walk down New York’s memory lane is now just a mouse click away.

The city’s Municipal Archives yesterday rolled out a new online site that gives the public access to a treasure trove of 875,000 historic photos of the Big Apple, with some dating back to the mid-1800s.

There are snapshots of Yankee slugger Babe Ruth — chomping on a cigar and signing autographs for fans — and dozens of dramatic black-and- white photos of the city’s bridges under construction.

There also are decades’ worth of photos of the city’s once-bustling and industrial waterfront.

The online gallery was such a hit on its first day that the site crashed yesterday on nyc.gov, the city’s official Web site.

Aside from viewing the archives for free, consumers can also buy high- quality reprints.

“Using 21st century tools, we’re making New York City’s rich, vibrant past more accessible than ever before,” Mayor Bloomberg said.