Leave Delhi by Volvo bus or private car/tempo traveller overnight toward Dehradun; buses commonly leave from ISBT Anand Vihar or Majnu Ka Tila. Overnight travel maximizes time in Mussoorie the next morning.
Start the day with fresh pastries, coffee and hearty breakfast at Landour Bakehouse or Emily's in Landour; both open around 8:00am and are perfect for a relaxed morning.
Visit Lal Tibba for panoramic Himalayan views and photo opportunities; the viewpoint is accessible any time, but mornings are clearest — plan ~45–60 minutes.
Stroll the flat, scenic Camel's Back Road along the ridge for relaxed walking and sunset potential; the route is open all day and great for a lazy afternoon.
Have a cozy dinner in the Char Dukan area of Landour (small cafes/pizzerias/bakeries) or choose an Indian restaurant on Mall Road; evenings are relaxed and pleasant.
If you want a short trek and panoramic views, head to Surkanda Devi (temple and viewpoint) — temple open generally early morning to evening; the hike takes ~1–2 hours round trip.
Visit Mussoorie Lake for a brief boat ride (boating normally available ~9:00am–5:00pm) or choose a last-minute souvenir stroll along Mall Road and the Tibetan market.
Drive down to Dehradun and board your overnight Volvo/bus or continue by private car toward Delhi; expect ~7–9 hours to reach Delhi depending on traffic.