Mount Meru is the best for acclimatization prior to Mount Kilimanjaro climbing; The Mountain is the 5th highest peak in Africa and is the second highest mountain in Tanzania at 4,568m.
For trips that have an emphasis on mountain climbing, you need to remember that even the easiest trekking involves some exertion, so you should be reasonably fit and sure that you will enjoy the activity.
Not recommended for pregnant travelers. Not recommended for travelers with poor cardiovascular health. Suitable for all physical fitness levels