A rail pass puts Europe at your feet. Imagination opens the way to adventure

TRAIN buffs enjoying the scenery from cozy compartments are pretty smug about their freedom from traffic and tour guides, from blizzardy or blistering weather. Indeed we are.

But now I've latched onto a further advantage in train travel: the extraordinarily versatile, small, plastic-covered rail pass. It is a true blank check for travelers in Europe who get their kicks dismantling an itinerary.

The ferry across the English Channel to Dover was delayed, giving me an extra 30 minutes in France. I stood on the Calais pier and let my imagination spin like a wheel with heady possibilities, but my thoughts kept returning to those creamy-soft, little-heeled Florentine pumps I had seen earlier on my trip.

Four days remained on my two-month Eurailpass. Why not? I grabbed my suitcase, dashed to Quai 3 and, with barely a skipped beat, was on my way back to Florence.

With the jubilation of a kid playing hooky on the first spring day, I collapsed into the compartment seat just as the train pulled out heading south. Chalk one up for solo travel, the freedom to bounce around on whim.

It was 3:45. I checked my Thomas Cook Continental Timetable and found I was on an express to Rome, with stops at Basel, Milan, Florence. Once again I was struck by the marvelous flexibility we rail-pass holders enjoy compared to other travelers. I would not have considered driving a rented car 1,000 miles down to Italy and 1,000 miles back for a pair of shoes, no matter how lovingly handcrafted. And air fare would have doubled the already steep price tag on that pair of shoes.

When the conductor slid open the compartment door, I bought a berth to Florence and changed cars. An extravagance, yes, but worth every centime, and it came with a complimentary breakfast in bed.

At 10:35 the morning sun sparkled on the Arno, and I made a beeline to the small shop on Via Tornabuoni, a tree-lined avenue of Renaissance palaces, fine stores, and offices, widely proclaimed to be ``one of the noblest, most perfect streets in the world.''

Settled on a pale green, velvet sofa, with my floppy handbag draped over a tiny gilt-rimmed end table, I asked for the scarpina marron'e, size 37.

The ambience of this shoe salon makes the most exclusive Rodeo Drive bootery in Beverly Hills seem garish by comparison. On display were fewer than 10 shoes. But there was no trace of snobbery in the maggiordomo. He smiled a touch wistfully and dispatched an assistant to a nearby dress shop. In a few minutes she returned carrying a beige wool skirt. I could sense their pain at contemplating the lovely shoes below the cuffs of my faded Italian jeans.

With the borrowed skirt -- Ah. Va benissima!

I held them gently in my hands, those sweet little tailored caramel pumps. For such perfection $110 did not seem out of line.

On an elegance chart I put Florence at the top, for here even the tourists appear to dress with more respect for the formally attired Florentines.

At last, properly shod and wool-skirted, I revisited my favorite places -- polished little heels clicking brightly on the marble floors of the Palazzo Vecchio, up the stone steps of the Bargello, echoing along the vast central aisle of the Dominican church of Santa Maria Novella.

Now, caught up in the fun of revisiting favorite places, I decided to catch the overnight to Munich at 8 o'clock.

The train was too crowded and noisy. After an hour I got off at Bologna and caught a sleeper to Vienna instead. More cheers for ad-lib traveling.

Sleepers offer a variety of accommodations, from inexpensive couchettes (facing triple-decker berths, mere shelves with blanket and pillow), to single bedrooms with wash basin, towels, soap, a carafe of drinking water, and a lock on the door. For exclusive use in a single or double bedroom the supplemental fare is about equal to a first-class hotel room.

The train arrived promptly at 9:10, giving me a whole day in Austria's dazzling capital.

It was Sunday; I had just time to taxi to the Hofburgkapelle to hear the Vienna Boys' Choir. They sing at early service every Sunday from mid-September to late June, but I'd always missed them. My new shoes glowed prettily in the candlelit chapel.

After church I decided to lunch in the rotating caf'e-restaurant atop the 826-foot observation tower in Danube Park. A clear day, a magnificent view of Vienna.

The day was topped off with a recital at Musikerein, home of the Vienna Philharmonic, before catching the 11 o'clock to -- well, why not? -- Venice.

On the Vienna-Venice express I had a couchette compartment all to myself. You'd seldom get a break like that during peak season. In fact, summer travelers often reserve seats or berths on the international trains before leaving home.

For my extra day in Venice, the new shoes were carefully stowed in my duffel while I slogged around in the cold drizzle in my dependable, old Wellington boots.

Happiness turned out to be that impromptu return to three cities I'd loved most during the planned part of my trip. A textbook example of serendipity. A plus on the solo travel scorecard.

One help on my quick trip was Thomas Cook's Continental Timetable, published 12 times a year, priced at $17 each in the United States, $8 in England. It requires a large coat pocket, but I was endlessly grateful for this travel aid.

Surprisingly useful for train travel is a radio or recorder with a headset. Once my compartment mate happened to be a stupefying nonstop talker. All I wanted was undisturbed contemplation of the Alpine scenery, so I offered him my headset plugged into the entire Beethoven Ninth, and gained for myself a full hour's grace.

It was a kick to run the tape of Schubert's ``Wanderer's Fantasy'' while strolling past the composer's statue in Stadtpark, and to switch to ``Tales From the Vienna Woods'' in a dark grove of pines -- but not easy to keep my pretty shoes from waltzing away on the grass.