How to shape three days
D1 Louvre + Tuileries (Orangerie is a fork); D2 Orsay or Pantheon + Luxembourg, or Vosges + one museum; D3 Abbesses uphill or one Champs stretch + one hall. Day-trips replace a full day. Follow official tickets.
Hard stops
Never Louvre + tower + Montmartre the same day. A Museum Pass saves queues — not multi-axis permission. One dinner room only.