John 18: 1-2.
When Jesus had spoken these words, He went forth with His disciples over the brook Cedron, where was a garden, into the which He entered, and His disciples.
And Judas also, which betrayed Him, knew the place: for Jesus ofttimes resorted thither with His disciples.
John does not specify that the garden was Gethsemane, but two other gospel writers did (Matt. 26:36 and Mark 14:32). The important thing here is that this was, apparently, a place where Jesus and the disciples often gathered; it is likely they frequently slept there when they were near Jerusalem. Jesus was making no effort to conceal Himself, but chose a place where He could easily be found. Judas knew the place well.
The brook Cedron (Kidron) ran down from the Temple, and at this point it would be colored red from the blood of all the passover lambs that had been sacrificed. There was a channel from the altar in the Temple that had been created for the express purpose of disposing of the blood and other refuse from the sacrifices. Crossing that brook must have been a vivid reminder to Jesus of His own sacrifice which was soon to come.