The outer part of Oslofjord forks into two and to reach Oslo itself, you will sail along the right-hand fork, known as Drøbak sound. About 10 miles long and half a mile wide, it's framed by forested hillsides. The town of Drøbak has served as the winter harbour for Oslo, as the fjord can sometimes freeze, cutting off access to the capital. It was also the site of a battle during World War II where the German forces were held back from invading Oslo, preventing Norway from surrendering. As you pass Drøbak, you're sailing over a road tunnel that dives to a depth of 134 metres below sea level.
The inner part of Oslofjord is dotted with islands, each with a tale to tell. Hovedøya, nearest the city centre, holds the ruins of a monastery. Lindøya is home to 300 brightly-coloured summer cottages. Gressholmen was the location of Norway's first main airport in 1927. Many of the islands have beaches, with Langøyene being a favourite with sun worshippers and swimmers.