As long as you're going to Helsinki for the Worldcon, why not make a vacation out of it? Finland is a beautiful country and the one tie I visited it, I loved every minute of it.
This is part of a continuing series.
Old Rauma is a UNESCO World Heritage Site, one of seven in Finland, and is quite possibly the single most laid-back to tour. It consists of some six hundred buildings in the core of the town, built between the Eighteenth and Nineteenth Centuries. (The city is much older but, as with so many other wooden cities, there was a fire.) The streets were laid out in medieval times, so they tend to be narrow and the buildings are vernacular -- in the style of earlier times. They are painted a variety of colors: reds, greens, yellows, blues, and ochres.
Rauma is a living city and most of the houses are inhabited, so you can't go tromping about in people's yards. But in a warm human touch, many people place items in their windows for decoration. I thought that very generous of them.
In Helsinki Square, there is a statue titled The Lace-Maker, a memorial to the fact that Rauma was once a lace-making center. But the pleasure in visiting Old Rauma is not historical but simply the gentleness of the experience: spending a few hours wandering about and getting to know a very old city, and gaining some sense of its soul.
I found the above photo at the Visit Helsinki site, which has tourist information far superior to anything I can give you. I believe (I could be wrong, though) that's the market square at the center of Old Rauma. But really the joy of the place is wandering through its medieval-narrow streets, seeing what there is to b seen.
You can explore the English-language version of the site here.
You can read what UNESCO had to say about it here.