Below is a ready-to-use 3‑night luxury-resort itinerary based on staying at a beachfront five‑star resort near Colombo (sample property: Taj Bentota Resort & Spa). I also list a few alternative luxury options if you’d prefer a city hotel instead. Times are approximate and I include booking/transport tips.

Summary recommendation

• Base yourself at Taj Bentota Resort & Spa (luxury beachfront resort with Jiva spa, multiple restaurants and watersports/concierge who can arrange river safaris and private dinners). (tajhotels.com)

Practical notes before you go

• Transfer from Colombo (or Bandaranaike Airport) to Bentota is typically about 1–1.5 hours via the Southern Expressway (depends on traffic; private car transfers are easy to arrange through your hotel or a local operator). If you prefer public transport there’s also a direct train option. (rome2rio.com)
• Book spa treatments, Madu Ganga (mangrove) boat safaris and any private beachfront dinners in advance with the hotel concierge (popular slots fill early).
• Bring reef‑safe sunscreen, insect repellent for mangrove trips, comfortable walking shoes for Galle, and swimwear.

3‑night sample itinerary (Taj Bentota as base)

Night 0 — Arrival / transfer day

• Afternoon: Arrive Colombo → private car transfer to the resort (allow ~1–1.5 hr). Check in; settle into a sea‑view room. (rome2rio.com)
• Late afternoon: Short beach stroll and welcome drink at the resort bar.
• Evening: Light 60–90 min Jiva spa treatment (signature massage to unwind after travel). Dinner at the hotel’s Sea View or S.H.A.C.K. (fresh seafood). (hoteles.com)

Day 1 — Mangrove cruise & lagoon highlights

• 08:00 – 09:00: Breakfast at The Palms (hotel restaurant).
• 09:30 – 12:30: Madu Ganga / Balapitiya boat safari (private boat): explore mangrove channels, “Cinnamon Island,” small island temples, optional fish‑pedicure stop and birdwatching. This is best booked through the hotel concierge as a half‑day private cruise. (maduriversafari.lk)
• 13:00: Return for a late lunch at the resort.
• Afternoon: Choose between relaxing by the infinity pool / beach, or an adrenaline watersports session (jet ski, banana boat, wakeboard) arranged by the resort/watersports operator. Bentota is a top spot for these activities. (riveradventure.lk)
• Evening: Optional private candlelit dinner on the beach (hotel arranges) or fine‑dining at Sea View.

Day 2 — Culture & Galle Fort half‑day trip, then spa/ayurveda

• 07:30 – 08:30: Early breakfast.
• 09:00 – 13:30: Drive to Galle Fort (about a 50–60 minute drive from Bentota) — enjoy a guided walk around the UNESCO World Heritage Old Town of Galle and its fortifications, visit the Old Dutch Hospital precinct, boutiques, galleries and the Maritime Museum. (You can choose a guided walking tour to learn the history and get best photo spots.) (rome2rio.com)
• 13:30 – 15:00: Lunch in Galle (many excellent cafés/restaurants inside or near the fort) and then return to the resort.
• Late afternoon: Book an Ayurvedic consultation or an extended Jiva spa ritual (90–120 min) to recover after the day’s walking.
• Evening: Sunset cocktails on the beach and a relaxed final‑night tasting menu at the resort.

Night 3 — Departure day

• Morning: Leisurely breakfast, final swim or beach walk.
• 11:00 – 12:00: Check out and private transfer back