While I have not been on Celebrity's version of the tour, from what I can gather from their tour description you will be transported across the Isthmus to the Visitor's Center at Miraflores Locks which is one of the original locks.  From there it is back to the Atlantic side to the Expansion Observatory Platform at the new Agua Clara Locks.  After viewing the operations there it is back to the ship in Colon.   Allow about an hour and half for the ride each way.  Actually the drive is c