The Mornington Peninsula is a roughly boot-shaped sliver of land south of Melbourne, framed on three sides by water — the calm, family-friendly waters of Port Phillip Bay on its inside curve, the wild Bass Strait on its ocean-facing back, and Western Port Bay separating it from Phillip Island. Each coast has its own character, and a single day tour can dip into all three.
What makes the Peninsula so loved by Melbourne locals — and by visitors who discover it — is the sheer compression of experiences. You can soak in 38°C geothermal pools at Peninsula Hot Springs in the morning, taste cool-climate Pinot Noir at Red Hill cellar doors at lunch, walk the cliff-top boardwalk at Cape Schanck Lighthouse in the afternoon, then photograph the famous bathing boxes at Mt Martha or Brighton on the way back to Melbourne. All within 75 km.
For travellers who don't want to deal with traffic on the Mornington Peninsula Freeway or the logistics of multiple bookings (hot springs, wineries, lighthouses), a guided Mornington Peninsula tour from Melbourne is by far the easiest way to do it well. You see more, drink wine without worrying about driving, and arrive back in Melbourne by dinner.