Gunung Agung is the highest and most sacred mountain in Bali. It offers spectacular views of the island, the surrounding sea, the 'Gilis', neighbouring Batur volcano, Lake Batur, and of Rinjani (3,726 m) on neighbouring Lombok island. Agung is a stratovolcano. There is no volcanic activity at the moment. The last eruption took place in 1963-64. It was one of the world's largest in the 20th century and caused extensive damage and many fatalities. The climb is not difficult or dangerous. It does not require any technical skills or special equipment, just good boots because the lower section through the rain forest can be very slippery when it is raining (and it can rain heavily for hours at any time of the year, even in the so-called 'dry season'). The ascent takes five to six hours. The best time for it is at night. Leave at midnight (or rather 11 p.m.) to make sure you arrive at the top before sunrise, not only to experience a beautiful sunrise but also to have the best chance of getting a clear view. Later the view is generally soon blocked by clouds coming up from the rain forest. Make sure that you bring a torch with you, and enough water (there is no water available along the route). You can climb Agung with a guide or without a guide. It is easy to find a guide at Besakih (just ask around). There is one point close to the treeline where you have to be careful not to miss the right turn.
You can put up a tent along the route, or do the climb in 9 to 11 hours (ascent + descent) without staying overnight on the mountain. There are no huts, and I do not remember seeing any shelters.
The starting point of the climb is Pura Pengubengan, which belongs to the famous temple complex of Pura Besakih on the south-western slope of Agung. Go to the main entrance of the Besakih complex (1,000 m), where you need to sign up for the climb, and then (on a new three-km-long road) on to Pura Pengubengan (1,250 m), which is the uppermost temple of the complex. At Pura Pengubengan you will find the trailhead. You can go there e.g. by chartered car with a driver. After the climb the car will pick you up at a prearranged time. There is another track up to the crater rim from Pura Pasar Agung (1,500 m) on the southern slope. It is shorter (about three hours) but does not go to the very top and you do not get the 360° view, but it is a very worthwhile climb as well. You get to Pura Pasar Agung by road from the village of Selat.
You need to sign up for the climb at the main entrance of the Besakih complex (please let me know in case this is no longer necessary). Climbing the mountain is not permitted when major religious events are being held at Besakih, i.e. mainly in April. For the Balinese, Gunung Agung is a holy mountain, and Pura Besakih is Bali's most important temple.
May - November (during the dry season; in April climbing is generally not permitted due to important religious ceremonies at Besakih) Climate
As for accommodation, close to Agung, you may want to check out this resort:
Gunung Agung Photos, PEAKWARE Photos by Nigel Easton Faszination Vulkane Volcano website by Rolf Cosar (in German) Global Volcanism Program By the National Museum of Natural History, Smithsonian Institution Mount Agung on WIKIPEDIA You may also be interested in climbing Mt. Sirung on Pantar Island.