Here are hotels (and a couple hostel‑hybrid picks) in Melbourne known for having the most social, lively atmospheres — grouped by the vibe they’re best for and with a short note why:

• Space Hotel (CBD) — rooftop terrace with hot tub, regular theme nights, lounge bar and a big communal kitchen; popular with solo and young travellers who want on‑site social spaces. (oyster.com)

• Ovolo (Laneways / South Yarra) — boutique, design‑forward hotels that run a daily “social” / apero hour (happy hour) in their lobby bars (good for meeting other guests), plus lively public bars nearby. Great if you want stylish, friendly boutique energy. (ovolohotels.com)

• QT Melbourne (CBD) — well‑known rooftop bar (Rooftop at QT) with DJs and a weekend party vibe; good for groups and nightlife without leaving the hotel. (cntraveler.com)

• W Melbourne (CBD) — big lifestyle hotel with a pool‑deck bar (WET) and regular Sunday/pool sessions; attracts a lively crowd and is set up for daytime‑into‑night socialising. (marriott.com)

• Prince of Wales / “The Prince” (St Kilda) — historic hotel that doubles as a live‑music and nightlife venue (Bandroom, bars and event nights) — excellent if you want live gigs and a real local nightlife scene. (en.wikipedia.org)

• Nomads / Base / Nomads St Kilda (hostel) — party/social hostel with an on‑site bar and nightly events (bingo, trivia, silent disco etc.) — the top choice if “meeting people” and nightly events are your priority. (hostelworld.com)

• The Cullen (Prahran) — art‑hotel with buzzy restaurants/bars and a rooftop event space; good for a creative, social neighbourhood vibe (Chapel St / Prahran). (cntraveler.com)

Quick tips to get the best social experience

• Go weekends or evenings (rooftop DJs, live‑music nights and hotel social hours usually run Fri–Sun). (cntraveler.com)
• Book rooftop or pool tables in advance — popular spots fill fast. (tripadvisor.com.au)
• If your priority is meeting other travellers, choose a social hostel/hybrid (Space Hotel, Nomads) over a luxury hotel; boutique hotels (Ovolo, QT) are better for a polished cocktail‑bar scene. (oyster.com)

If you want, I can narrow these to a specific neighborhood (CBD, St Kilda, South Yarra/Prahran), a price range, or check current event nights and rooftop bookings for particular dates.