What fits into a short Paris trip depends less on which sights you choose than on how far apart they are. The city's geography, not your list, sets the limit.
One day
One major museum and one walking axis. Not both ends of the city.
Version A — the right bank axis
The Louvre at opening on a booked slot, two hours in one wing. Out through the Tuileries, past the Orangerie. Place de la Concorde, the Champs-Élysées, and up the Arc de Triomphe for the best view in the city.
Version B — the left bank and island
The Musée d'Orsay, then across to the Île de la Cité for Sainte-Chapelle and Notre-Dame's exterior, then the Latin Quarter, the Panthéon and the Jardin du Luxembourg.
Adding Montmartre and the Eiffel Tower to either means spending the day underground.
Two days
Do both versions above.
Then add one of the two remaining icons in an evening: the Eiffel Tower, best from the Trocadéro across the river at dusk, or Montmartre and the Sacré-Cœur at sunset.
Two days covers the essentials without depth. Most people leave wanting a third rather than feeling finished.
Three days
The third day is where Paris stops being a list of monuments.
The Marais — Place des Vosges, the Picasso Museum, the Musée Carnavalet (free), the Jewish quarter on Rue des Rosiers, and the covered passages a short walk north.
Or Versailles, which needs most of a day — RER C, timed entry, and the gardens which are free on most days and enormous.
Or Père Lachaise and the eastern arrondissements — Belleville, Canal Saint-Martin, the 11th.
A week
Add the small museums that would headline other cities: Jacquemart-André, Rodin (the garden ticket covers most of the famous works), Cluny for medieval art in a Roman bath.
Add a day trip: Giverny for Monet's garden, Chantilly for a château with the second-best art collection in France and no queue, or Vaux-le-Vicomte, which inspired Versailles.
The distances
| From | To | Metro |
|---|---|---|
| Louvre | Eiffel Tower | ~25 min |
| Eiffel Tower | Montmartre | ~35 min |
| Montmartre | Latin Quarter | ~30 min |
| Marais | Père Lachaise | ~15 min |
Three such crossings in a day is two hours underground, which is the arithmetic that ruins short Paris trips.
Practical
Ten to fifteen kilometres a day on a sightseeing itinerary. More than people expect.
Alternate walking with short metro hops rather than walking everything or riding everything.
Book the Louvre (required even with a pass), the Eiffel Tower summit, Sainte-Chapelle and Versailles.
Lunch, not dinner — the formule midi is roughly half the evening price.