Like a classic secret passage with pistons, but with the difference that there are also tracks here.

On the screenshot the secret passage is open. Closed it is only an inconspicuous curve.
This secret passage can be used, for example, to lose pursuers of a mine cart. This can be useful in a player trap, for example, where the player's items are subsequently taken away and you want to prevent the former owner from finding them again.

Instructions:

The back (when closed):

Note the settings and directions of the repeaters! The many repeaters are necessary so that the order in which the pistons extend is reversed to the order in which they retract.
The site:

There is also a currently extended piston under the passage. All pistons are sticky. The redstone signal is reversed on all pistons except the piston that pushes the rail, which is later in the passage.
After you have built this so far, you can still flip the switch or connect something to it, such as a memory cell or a toggle circuit.

The Redstone circuit does the following when opening the secret passage: first, the two pistons holding the blocks that close the passage retract. Then the rail is pushed in from the side that connects the two tracks. The last thing to do is to remove the signal at the turnout, otherwise it won't connect automatically.
When you close the secret passage, it happens the other way around.