Mount Batur is a good place. Combine it with friendly guide, and you'll get that amazing experience. The hiking takes about 2 hours and a half for going up and about 1 hours and 40 mins for going down (duration may vary depends on how often you stop for rest. haha:) ). As it is a mountain, cold environment is something you can expect; therefore, it is strongly recommended for you to bring additional blanket, jacket, or anything to keep yourself warm once you reach the top. Don't forget to bring yourself a good camera (or phone with good camera quality) cause the view up there is breathtaking. Very recommended for people who like mountain, hiking, etc.