Collect your rental at Calais or nearest airport/agency; inspect the vehicle, verify insurance (cross-border coverage) and add a fuel/toll plan as needed.
Park in a central Parkhaus (look for 'Parkhaus Dom') and walk to the cathedral; note some German cities have low-emission zones (Umweltzone) requiring a sticker.
Explore Germany's iconic Gothic cathedral; open most days and the tower climb (if available) offers panoramic city views — cathedral hours often from 6:00 to evening, tower 10:00–18:00 seasonally.
Try Kölsch beer and hearty Rhineland dishes at this classic brewery-restaurant right by the cathedral — lively and convenient for drivers (short park walk).
Visit the Chocolate Museum (open ~10:00–18:00) for sweet history, or take a scenic stroll along the Rhine for sunset views — both are easy from central parking.
Fuel up and depart west toward Brussels via A1/E40 (approx. 210 km, ~2h15 drive); Belgium does not have motorway tolls for cars but watch city LEZ/low-emission rules for Brussels.
Use a central car park (Q-Park near Grand Place) then walk to admire the ornate guildhalls of the Grand Place — the square is open any time for external viewing.
Arrive at the Markt square and climb the Belfry for panoramic medieval city views; tower usually open 9:30–18:00, allow time for the queue and 366 steps.
Head west via A17/E40 then A16 (approx. 140 km, ~1h45), plan for fuel and any final tolls in France as you re-enter, and give extra time for border checks if crossing busy routes.