Grand Central Station's approaches probably have the most puzzle switches in the smallest volume of railroad anywhere. Engineers aproaching the terminal are given a track number and a permissive signal and sent on their waythey have to trust the tower operators who line them up as it is impossible to have a signal at every switch. All of this is in a tunnel filled with columns and walls with several movements taking place simultaneously. The avrage train move might encounter 15 of these switches.
JAY and HALL interlockings outside the Jamaica Station of the LIRR are probably the next most hideous location since there are three possible routings east and west plus platform and bypass tracks. You wouldn't want Dan to Dash for the wrong train, would you?
A much simpler implementation of a double slip can be found at the Seashore Trolley Museum in Kennebunkport Maine. The double slip is a point - mate design, and is set up to sort passenger trips from certain yard moves. On a normal summer day at least three of the four possible moves will be made in both directions. The fourth possibility will come up maybe every other day. Although the switch is quite forgiving, failure to read the switch correctly has slowed down the qualification of many an operator. The switch is right in te middle of the public area and is easily photographed.
While you are there check out the unique "Freddy" switch at the south end of Riverside Barn. It is one of those situations where you have to make do with the materials available. The frog is probably two sizes smaller than the rest of the switch, thus there are some horrendous looking curves. Despite this it is not derailment prone. "Freddy" was Fred Perry who had a reputation for taking on impossible tasks with acceptable if not asthetic results. His talents were applied to many of the historic trolley operations running around the country. He passed on before his time about three years ago.
The next stop is Washington. Change for Forest Hills Trains on the Winter St. Platform, and Everett Trains on the Summer St. Platform. This is an Ashmont train, change for Braintree at Columbia.