To celebrate the last wintry moments of the year, I've been for a walk on the Baltic. There weren't many people out there; just a few old men dressed up in thick, padded overalls, angling for fish through holes they'd drilled through the ice. The wind was blowing snow into our faces. It was extreme.
About 70 kilometers (40 miles) across the sea from Helsinki is Estonia but, even with a flask of hot soup, I couldn't have reached it. So many ships sail along the middle of the Gulf of Finland that it never has a chance to freeze solid.
It hasn't always been so. People have been skiing between Helsinki and Tallinn for centuries. In the late 19th century, when Estonia was part of the Soviet Union, defectors tried to get out that way.
In March 1947, an Estonian called Heino Mikiver set out on his skis from Pirita, just east of Tallinn. When he reached the fortress just off Helsinki two days later, the Finns arrested him and sent him back. Many others continued to try until the 1990s, when Estonia regained its independence.
Some winters the sea doesn't freeze at all. This winter began like that. The high-speed catamaran ferries between Helsinki and Tallinn can't handle ice and usually cease services in the autumn. This time they continued until the middle of February, when temperatures suddenly plunged.
For a few days we had conditions that skaters dream of. The sea was covered by clear ice with no snow on it. Ice hockey rinks are about 60 metres (66 yards) long, and even in Olympic speed skating, the oval is only 400 metres. Imagine a natural rink that's so long that it reaches over the horizon.
Snow came at the start of March so now we either have to trudge across the sea or put on skis. In either case it's quite safe. Just ten centimetres of clear, solid ice will easily bear the weight of a man. All the coastal islands are now just a stroll away.
It's true that people fall through the ice every year and some of them drown. You don't always know how thick the ice is, especially when there's snow on top. You can't tell by looking if it's clear and strong — what the Finns call teräsjää, steel ice — or weak, porous stuff. But if the weather has been really cold for weeks on end, you're okay.
When in doubt I wait till someone else comes along, preferably someone really overweight. Then I follow at a respectable distance. Penguins in the Antarctic do the same thing when they fear there may be killer whales in the water. In fact I've heard they don't wait but try to push a neighbour in. I don't do that.
When the ice is solid and 15-20 cm thick, it will take a car. Driving on the sea might seem to be the ultimate death wish but 30 centimetres of ice will support a loaded lorry. Until 1986 there was even a public bus route in winter between Helsinki and the island fortress of Suomenlinna.
Fortress is a misleading word. It is a big place at 80 hectares (200 acres), but it has been useless in times of war. In spring 1808, when it was attacked by the Russian army that had already occupied Helsinki, it surrendered. The defenders marched out of the fortress, over the ice, and the Russians marched in the next day.
The spring equinox comes next week. After that, the days will be longer than the nights and the sea ice will start melting fast. By the start of April, there will be only a few floes left in the green water. When the first cruise ship arrives at the start of May, the frozen sea will be a distant, and faintly incredible, memory.
Pat Humphreys, 9 March 2009