Here are highly regarded conference / MICE venues in Colombo, with a short note on size and best uses so you can pick by capacity, location and format:

• Bandaranaike Memorial International Conference Hall (BMICH) — large purpose-built conference & exhibition complex (many halls, breakout rooms; suitable for international conferences and trade shows). (en.wikipedia.org)

• Shangri‑La, Colombo — very large, flexible ballrooms (including a ballroom that can be 1,580 m² and be subdivided), extensive meeting rooms and outdoor lawn options; great for large plenaries, banquets and segmented breakout sessions. (shangri-la.com)

• Cinnamon Life / Cinnamon Life Convention Centre — brand‑new large integrated convention spaces and ballrooms (huge main ballroom and exhibition capacity), good for very large conferences & exhibitions. (cvent.com)

• Cinnamon Grand Colombo — multiple ballrooms and meeting rooms (large Oak Room / Grand Ballroom), strong hotel‑support for conferences and accommodation. (cvent.com)

• Cinnamon Lakeside Colombo — several grand ballrooms, boardrooms and a unique lakeside “floating” venue; excellent for mid‑to‑large conferences and evening functions. (cinnamonhotels.com)

• Hilton Colombo (connected to World Trade Centre) — pillar‑free ballroom and flexible meeting spaces with modern A/V; convenient for business districts and hotel accommodation. (hilton.com)

• The Kingsbury Colombo — large ballrooms (Balmoral, Victorian, etc.) and harbourfront location; good for banquets and conferences of several hundred. (discovercolombo.com)

• The Galle Face Hotel — historic central hotel with a range of meeting rooms and ballrooms (suits executive meetings, mid‑size conferences and gala dinners). (gallefacehotel.com)

• Water’s Edge (Battaramulla, near Colombo) — large column‑free grand ballroom(s), many meeting rooms and large-capacity banquet/theatre setups; excellent for large national conferences, expos and gala events. (watersedge.lk)

• Sri Lanka Exhibition & Convention Centre (SLECC) — dedicated exhibition hall (≈3,700–4,000 m²) and multipurpose halls for trade shows, expos and conferences. (en.wikipedia.org)

• Nelum Pokuna Mahinda Rajapaksa Theatre — performing‑arts venue with a large auditorium (~1,200–1,300 seats); ideal if you need theatre‑style plenaries, keynote talks, or high‑end stage production. (en.wikipedia.org)

Quick selection tips

• For exhibitions / very large delegate counts: SLECC, Cinnamon Life, BMICH or Waters Edge. (en.wikipedia.org)
• For hotel‑based conferences with guest rooms and A/V support: Shangri‑La, Cinnamon Grand, Cinnamon Lakeside, Hilton, Kingsbury, Galle Face. (shangri-la.com)
• For theatre‑style staged events: Nelum Pokuna. (en.wikipedia.org)

If you tell me: expected number of attendees, preferred dates, and whether you need on‑site accommodation, exhibition space, or theatre staging, I can narrow this list to 2–3 best fits and pull contact/quote pages or floor plans for those venues.