There's plenty to keep you active in Malawi. As you might expect in a country dominated by a lake, there are many water sports available. The lake's population of colourful fish and warm, generally clear water make for great scuba diving and snorkelling. Many of the more up-market places along the lake have facilities for water skiing and windsurfing. You can also go sailing - there are even luxurious 'sail safaris' where all you have to do is dangle your toes in the water.
Malawi has several national parks and game reserves where wild animals and birds can be seen from the comfort (and safety) of a vehicle, or from horseback or on foot. In addition to the parks and reserves, the Elephant Marsh is an excellent place for birding; it's a large area of seasonally flooded plain on the Shire River, about 60km (40mi) south of Blantyre.
There's fine hiking in Malawi. The main areas include the Nyika Plateau (in the north of the country) and Mt Mulanje (in the south). Rock climbing is very popular at Mt Mulanje.