A clear fishing wire is tied around the island of Manhattan - being attached to posts around the perimeter, from 1st street to 126th. Part of an eruv, it's a Jewish symbolic enclosure. Established almost 2,000 years ago it allows Jews to more realistically follow the laws of Sabbath - a day of rest

An Eruv Encircles Manhattan To Allow Observant Jews To Leave Home On The Sabbath : NPR

[...Most people walking on the streets on Manhattan do not notice it at all. But many observant Jews in Manhattan rely on this string in order to leave the house on Sabbath.

According to the laws of Sabbath rest, nothing can be carried from the domestic zone into the public zone on Saturday. That means no carrying house keys or a wallet. It also means no pushing a baby stroller. For parents of young children, no carrying would mean not leaving the house on Saturday.

The eruv symbolically extends the domestic zone into the public zone, permitting activities within it that would normally be forbidden to observant Jews on the Sabbath. ...

... and many others rely on the eruv every Saturday to leave the apartment with their children. Luckily, Manhattan's eruv has never been down. Rabbi Mintz, co-president of the Manhattan Eruv says, "It has never been down for a Sabbath. Never. We always save it at the last minute." Mintz noted that the Macy's Thanksgiving Day parade is always a particularly trying time.

More than two hundred cities around the world are partially encircled by an eruv. Manhattan's certainly isn't the largest, but according to Rabbi Mintz, it's the most expensive eruv in the world. It costs between $125,000 and $150,000 a year to maintain. Rabbi Mintz helps raise the funds every year from synagogues and private donations

Every Thursday before dawn, a rabbi drives the perimeter checking to see if wind or a fallen branch has broken the line. There are usually a few breaks so a construction company is called and the rabbi gets in a cherry picker with fishing line in hand to repair the eruv. That's the part that costs so much.

As it turns out, resting on the Sabbath takes a lot of preparation. Dina Mann says the eruv does more than just help her enjoy a Saturday walk in the Central Park, it lets her enjoy the Sabbath. "

There'a a warmth in the house the minute you light the candles because you're rushing, rushing, rushing, making sure all the lights are on, making sure the candles are in there, making sure all the food is cooked... Then you just light the candles and just like let go of everything." ...]