I'm leaving on a jet plane and I've no idea where it's headed. The envelope containing my ticket and itinerary remains sealed. My bag is packed with swimmers and scarf, sundress and beanie, socks and thongs, for temperatures at the extremes of the Australian continent can vary wildly at this time of year. I can't risk the discomfiture of strolling the Whitsunday promenades in woollens or shivering through Hobart's autumn chill.
The moment of reckoning comes as I approach the Virgin check-in desk. I've averted my eyes from the departure board and now relish my final moments of ignorance. The check-in attendant asks me where I'm going.
"I've no idea," I say.
She unfolds the voucher I've handed her and braces for the big reveal: "Adelaide!" she exclaims.
There's something thrillingly fatalistic about allowing someone else to determine one's holiday destination. I'm travelling on a mystery flight, an old concept that has been revived and smartened up by Mystery Flights, a company which offers day trips to 15 destinations and longer packages to 21 cities around Australia.
The fundamentals of my journey have been taken care of: flights, hotel, airport transfers. But while my now-unsealed dossier is brimming with information about Adelaide, how I spend my time there is entirely up to me. It's an act of faith that will severely test my sense of adventure, since I'm familiar with the city and must seek out new encounters beyond its shopping boulevards, chocolatiers, sublime eateries and tree-framed, church-spired skyline.
My quest for the unpredictable is alerted by a brief reference in my Adelaide visitor's guide to the world's only inner-city dolphins, which inhabit the Port Adelaide River. There are no dolphin cruises scheduled for the days I'm in Adelaide, but I'm not deterred. I walk to the railway station on North Terrace, figure out its complex ticketing system and catch a train.
Leaving the city behind, I travel north-westwards, past provincial-looking stations called Kilkenny and St Clair and Alberton. At Port Adelaide I disembark and follow my map all the way up Commercial Road, stopping to read memorials set into the pavement in tribute to the local Aboriginal people: "Ancient spirits live in this land," says one; "Begin by stepping forward," urges another.
It's mid-afternoon and Port Adelaide is a sleepy, unexpected delight: I had anticipated grungy industrial streetscapes but have been met instead by restored 19th-century buildings reclining beneath a boundless blue sky. In the visitor's centre, I find a map of the precinct's Heritage Walking Tour and weave my way through its narrow streets, past the Royal Arms Hotel, the Professional Fishermen's Memorial and the lighthouse which was built beside the river in 1869.
I stand beside the waterway for an interminable time, scouring its surface, willing the dolphins to appear. Defeated, I find respite from the afternoon warmth in an art gallery. A local woman strikes up conversation.
"Have you seen Semaphore yet?" she asks. "No? I knock off in 20 minutes – meet me back here and I'll take you there."
Yielding again to the unpredictable, I find myself climbing into her car 20 minutes later and sailing across the Birkenhead Bridge. Aware that I've come here in search of dolphins, she slows as we cross the water; still, it keeps its secrets hidden.
But as we drive towards the seaside town of Semaphore this stranger – Annie is her name – brings the dolphins to life. She tells me the story of a male who was placed in the local dolphin marina (now closed) while he recovered from an illness. He learned from the performing dolphins how to tail-walk and, when he returned to the mangroves, taught some of the other dolphins his new party trick.
"Someone got a photo of him tail-walking, and – I'm telling you! – he's looking out of the corner of his eye at the camera [as if to say], 'Okay, have you got the picture?'"
Abutting Semaphore, the Gulf of St Vincent is a millpond of liquid pewter. Annie pulls into a parking lot and we take off our shoes and plunge our feet into the still-warm sea sand. This place, of which I've been ignorant, captivates me: walkers pick their way along the shoreline; locals take sundowners on the esplanade; a woman sets up her tripod in the shallows and poses for a self-portrait against the shimmering silver sunset.
My mystery flight, it seems, has set me on a journey of rediscovery: I'm seeing Adelaide with brand-new eyes.
*While Billy the dolphin was recovering in the marina, it was discovered that he was, in fact, female. She has been renamed Billie. For more about the dolphins, see portriverdolphins.com.au.
Mystery Flights depart daily from Sydney, Brisbane and Melbourne; departures from Perth and Adelaide are subject to availability. Packages range from day trips to three-night luxury trips and start at $295 per person; see mysteryflights.com.au. For information on dolphin cruises contact the Port Adelaide Visitor Information Centre; portenf.sa.gov.au/tourism.
The writer was a guest of Mystery Flights.