Mai Chau doesn't have a tourist service per se, and surprisingly few of the locals speak enough English to offer any advice or services, so if you want to make the most of the trekking opportunities in the area your best bet is to book a tour from Hanoi.
Tours range from one day -- a long day -- to longer treks covering Pu Luong Nature Reserve. We've heard good things about operators such as Mai Chau Trek and Mai Chau Tours but have yet to try them out ourselves.
If you're travelling independently you can either take yourself on a walk or bike ride around the surrounding countryside -- bicycles are available all over the villages for 20,000VND per hour -- or check out the activities organised by Mai Chau Lodge, which include rock climbing, kayaking, cycling and trekking.
Mo Luong (Soldier's) Cave, opposite Mai Chau Lodge, is one tour Mai Chau Lodge lists, but it's perfectly do-able independently, and to be honest, we were underwhelmed.
Another option is to head to Hoa Binh lake and try to persuade one of the fishermen to take you out on a boat. To get there, head back out of town until you reach the main road and then turn left, towards Son La -- rather than back towards Hoa Binh. Take a right at the next fork in the road.
Mai Chau Trek
Mai Chau Tours
Mai Chau Lodge