Collect your hire car in the morning and head east towards Porvoo. Founded in the 14th century, Porvoo is Finland's second oldest town, and for centuries it has drawn and kept artists. Among them was the national poet Johan Ludvig Runeberg, whose home is now a museum that shows how everyday life was lived in the 1800s.

Porvoo is not quite coastal, but the Porvoo River links it to the Gulf of Finland. Along the water stand the town's best-known landmark, the red wooden warehouses. By tradition they were first painted red for the arrival of Gustav III of Sweden. In practice they long served trade, storing goods and provisions brought from far off.

Explore the old wooden town on foot, look into the small shops and stop for morning tea in one of the cafes. Then continue east to Kotka, a town with a strong maritime history and, today, award-winning parks and gardens. If Finland's waters interest you, visit the Maretarium, devoted to the country's aquatic life, with more than 50 native fish species across 22 themed aquariums. Its centrepiece is a cylindrical tank of 500,000 litres and seven metres deep, the average depth of a Finnish lake.

There are a few more stops on the way to Lappeenranta. Hamina, Finland's oldest garrison town, was established in 1653, and its military past is still legible in the radial plan and fortifications. For more of that history, the Bunker Museum at Virolahti and the Salpa Line Museum at Miehikkälä sit about 13 km apart.

Arrive in Lappeenranta in the early evening and check in.

Lappeenranta is one of Finland's loveliest summer towns, known for its Karelian warmth and its position on Lake Saimaa. It is a border town with a layered history, long caught between two cultures.

The Fortress is the town's centrepiece, and the day is yours to explore it. The Swedes began fortifying Lappeenranta in 1721, as part of a defensive line that also took in Suomenlinna at Helsinki and the fortress of Hamina. In those years Sweden-Finland and Russia fought often, and the fortress changed hands between them. What stands today rests mostly on the works of the late 18th century, and the site remains lived-in and busy.

The Saimaa Canal is the other mark of this border. Opened in 1856, it ran between Lappeenranta and Viipuri, now Vyborg in Russia, both then within the autonomous Grand Duchy of Finland. In the Moscow Peace Treaty of 1940 the Karelian Isthmus and Vyborg were ceded to the Soviet Union, which split the canal and ended its traffic. In 1963 the Russian section was leased back to Finland, with a further 50-year extension agreed in 2013. The canal runs 43 km, and its eight locks manage a difference of 76 metres between the Gulf of Finland and Lake Saimaa.

In the evening, join a three-hour dinner cruise through part of the canal and out onto Lake Saimaa, in the long light of the White Nights.

After breakfast, drive on to Imatra, just 6 km from the Russian border. The town has drawn visitors for over 300 years, largely for the rapids of the River Vuoksi. In 1903 an Art Nouveau castle, now the Imatran Valtionhotelli, was built beside them to house travellers from Saint Petersburg. You spend the night here.

Your guide meets you in the lobby. After a short tour of the castle, you continue to the Crown Park, Finland's oldest nature reserve, established in 1842, where the story turns to the Grand Duchy and the golden age of 1800s tourism. Note that the tour involves a good many stairs.

The rest of the day is your own. Alvar Aalto's Church of the Three Crosses, completed in 1958, is recognised by DOCOMOMO as one of Finland's most significant works of modern architecture. The hundred-year-old district of Niskalampi and its small museum show how factory workers once lived. About 20 minutes away, the village of Ruokolahti is where the painter Albert Edelfelt sketched "Women of Ruokolahti on the Church Hill" in 1887; the church hill, with its wooden church and shingle-roofed belfry, is a fine place to pause. If a second castle appeals, Rantalinna, built on Lake Saimaa in 1913 as the summer residence of the Oldenburgs, serves lunch.

Drive on towards Punkaharju. Its ridge, with pine trees framing views of glinting water, has been a celebrated Finnish landscape for more than two centuries, described by both Runeberg and Topelius.

Begin at Lusto, the Finnish Forest Museum, a museum and science centre devoted to the long relationship between Finns and their forests. About 75 per cent of Finland's land area is forest, making it the most forested country in Europe. The forests are a livelihood, but also where Finns hike in summer, ski in winter and gather berries and mushrooms in autumn. Under the principle of Everyman's Right, anyone may walk freely in them, whoever owns the land.

To understand what that means in practice, we have arranged a private guided tour, covering the main exhibition and then a two-hour walk along Punkaharju Ridge to the Punkaharju Arboretum, home to 134 species and varieties of tree. Afterwards, lunch at Lusto or at Hotel Punkaharju, whose wooden main building, high on the ridge, opened in 1845 as quarters for foresters and lodging for travellers.

From here the road runs north to Joensuu, the regional capital of North Karelia, founded in 1848 by Tsar Nicholas I. The River Pielisjoki has always been its heart, once carrying steamboats, barges and floated timber in the golden age of river trade. The Carelicum, a museum and cultural centre by the market square, is a good introduction to the region. Karelian cooking rewards the curious, built on slow-cooked dishes, the produce of the forest, and pies and pasties for both everyday and festive tables. Many Joensuu restaurants serve a Karelia à la Carte menu of regional dishes made from local ingredients.

Today you visit Koli, one of the most striking corners of North Karelia. Finland's national parks were created both to protect nature and to give people somewhere to rest in it. The 40th was opened in 2017 to mark a century of independence, and more have followed since.

Ask a Finn about national parks and most will picture one thing: the view over Lake Pielinen from the top of Ukko-Koli. It is the country's best-loved landscape, and it has drawn artists for generations. Under Russian rule, the search for Finnish roots led people to these lands, rich in Karelian song and poetry. The painter Eero Järnefelt came to Koli often, sometimes with the composer Jean Sibelius, and it is thought that Sibelius's Fourth Symphony owes something to those visits. Pekka Halonen painted here too.

Meet your guide at the Ukko Nature Centre. There is some uphill walking, as the park rises to 347 metres above sea level, but the paths are made and the pace is gentle. Back at the centre, the exhibitions and a short film round out the day before you return to Joensuu.

Before leaving Joensuu, take in the market square and the Artisan's Quarter, Taitokortteli. In summer the square is the place to buy Karelian pies, the rye pastry with a rice filling that you can learn to make later on the tour. The Artisan's Quarter, a cluster of wooden houses given over to craft studios and shops, includes Café Kauppaneuvos, worth a stop for its pastries.

Drive west to the New Valamo Monastery at Heinävesi. Around 62 per cent of Finns belong to the Lutheran church, which holds a national status alongside the Finnish Orthodox Church and its roughly one per cent of the population. Historically, most of Finland's Orthodox Christians lived here in Karelia. During and after the Second World War, as the region became a battleground and much of it passed to the Soviet Union, many fled deeper into Finland. The original Valamo Monastery, once home to more than a thousand monks, was abandoned, and a new community was founded on an estate near Heinävesi.

A guided tour introduces the Orthodox traditions and the rhythm of monastery life, and includes a tasting of the wines the brotherhood makes on site. You might stay for lunch at the monastery restaurant, walk the grounds, or simply rest in the quiet.

From Valamo, continue to Puumala and Sahanlahti Resort, where dinner is available at the hotel, payable locally.

Join a Finnish guide for a seal safari through the Puumala archipelago aboard an electric Ecoboat. The solar-powered, weatherproof vessel runs almost silently, which suits the search for the Saimaa ringed seal, one of the most endangered seals in the world.

The rest of the day is yours. Take in Lake Saimaa from your private terrace, with its seating area and heated pool, or borrow the bicycles and rowing boats to move at your own pace between the villa and the Sahanlahti restaurants.

Today's drive runs through the countryside to the Pulkkilanharju Ridge, a line of islands joined by three bridges, with wide views across the lakes. The eight-kilometre chain was formed during the last ice age, roughly 12,000 years ago.

On the way, stop at the village of Kalkkinen and the Pihamaa Berry Farm, which makes award-winning berry wines. Buy fresh produce and take refreshments at the farm café.

After the bridges, continue to Lahti. For those drawn to modern architecture, the Sibelius Hall opened on the Vesijärvi waterfront in 2000; its architects, Hannu Tikka and Kimmo Lintula, took the Finnish forest as their starting point. You can drop in for lunch at the café, or arrange a private guided tour. Lahti is also a winter-sports town of long standing. In summer the observation deck at the top of the ski-jump tower offers a wide view, reached by chairlift or by car, and the Ski Museum sits at its foot.

Continue to Helsinki and return your hire car, or extend your stay.