Ranau is associated with the infamous and tragic Death Marches which occurred at the end of WWII in 1945. Over 2500 Australian and British POWs died at Sandakan and on forced death marches to Ranau.
Mesilau Park is on the slopes of Mount Kinabalu, accessible by a tarred road from Kundasang. They conduct guided 40-minute walks through a protected area which abounds with pitcher plants and orchids at 7am and 11am, and sometimes in the afternoon too. The morning walk is best for seeing wildlife. It is also possible to climb the initial section of the route up Mount Kinabalu, or to walk the whole way to the summit along an alternative route to that taken from the Park HQ. At 2,000m, it is a very cool, temperate climate with a lovely landscape, and quite different flora and fauna to the lower regions of Mount Kinabalu. There is a very nice (albeit slightly expensive) cafe with good views (coffee Rm11, lunch Rm15+), and it's possible to see lots of birdlife from your table. Rm15 conservation fee is charged at the entrance for foreigners (Rm3 for Malaysians). Accommodation is available from Sutera  (Rm135 - Rm2600 per room/lodge per night - 2-6 people)
Sabah Tea Garden offers light refreshments and meals overlooking the valley and mountain. Tours of the tea factory and gardens are offered. There is accommodation available in longhouse-style facilities. Although the tea is marketed as organic, realistically it is a very small section that is organic, and as it is grown alongside non-organic plants, cannot really be considered to be truly organic. It is a decent black tea, however, and you can buy it everywhere in Sabah. There is a small gift shop attached to the cafe. There is a small memorial to British and Australian troops who died on the Sandakan Death Marches next to the cafe.
Sungai Moroli Fish Spa is located next to the Tea Garden. It is a community venture, in which you walk into a river armed with fish food, and allow some very big fish to nibble at your toes for 15 minutes. Not as relaxing as a posh fish spa in Europe, but interesting, nonetheless. Not for the faint-hearted or thin-skinned!