Indonesia is often referred to as the world's largest archipelago, a name which aptly represents its 17,000 or so islands which span more than 5000 km (around 3,200 miles) eastward from Sabang in northern Sumatra to Merauke in Irian Jaya. If you superimpose a map of Indonesia over one of Europe, you will find that it stretches from Ireland to Iran; compared to the United States, it covers the area from California to Bermuda.

There are eight major islands or island groups in this enormous chain. The largest landmasses consist of Sumatra, Java, Kalimantan (Borneo), Sulawesi (Celebes) and Irian Jaya (the western half of Papua New Guinea). The smaller islands fall into two main groups: the Molluccas to the northeast, and the lesser Sunda chain east of Bali. Bali is a unique island, which for a number of reasons can be put into a class of its own.

Mountain lovers will find plenty to enjoy in Indonesia. A great volcano chain, the Bukit Barisan, runs the entire length of Sumatra. On the West Coast, the mountains fall abruptly to the sea, while to the east they ease gradually down to plains in a broad fringe of coastal mangroves. Vegetation-clad volcanoes also rise dramatically from the sea at Banda, Ternate and Makian. Many of the volcanoes are still active, constantly smouldering and occasionally erupting violently, though geological stations monitor the active ones constantly and give warning if they are unsafe to climb. Mount Merapi in Central Java is a favourite for climbers, despite being one of the most active on the archipelago.

Mountain lakes are also abundant in dormant craters of many volcanoes, the most famous of these being lake Toba in the northern highlands of Sumatra. This mountain lake covers an area four times the size of Singapore. In Kalimantan, waterborne transportation moves cargo and passengers up and down the major rivers: Mahakam, Barito, Kahayan and Kapuas. The mountainous island of Flores is famous for its multi-coloured volcanic lakes, known as Keli Mutu. The three lakes are in a close group and range from dark red to turquoise.

Located between two distinct bio-geographic groups - Asia and Australia - the flora and fauna of the archipelago is also quite idiosyncratic. Species found nowhere else on earth have flourished in certain areas, including the famous Komodo dragon on the island of the same name. Also in abundance are rare flowers, including exotic orchids, unusual insects, birds of paradise and numerous indigenous spices such as cloves, nutmeg cinnamon, mace and many more.