Although it is not possible to camp independently in Gunung Leuser National Park due to the law requiring an official guide, you can nevertheless arrange camping trips with your guide so that you can experience the sights and sounds of the rainforest from the [dis]comfort of your own tent!
For those that are a little squeamish and do not like the idea of sleeping on the jungle floor, there are basic lodges and guesthouses around the outskirts of Gunung Leuser, at towns like Ketambe, Bukit Lawang, and Tangkahan. Accommodation in these parts are not known for their luxury, but then again you should know that before arriving! You should have running water in your guesthouse, and perhaps a ceiling fan, but there will not be any air-conditioning or WIFI, so those ‘mod-cons’ you enjoyed in Medan are now long gone!
It is claimed that there are no mosquitoes in the park, although you need to make up your own mind as to whether anti-Malarial tablets will be required for your visit. I guess it’s best to err on the side of caution, but then again, you may have side-affects from taking these tablets, so it’s all a matter of preference. Your guide may even suggest that sleeping outside of the tent, completely at the mercy of the rainforest, is perfectly safe because of the supposed lack of mosquitoes, yet this is still not advisable due to other dangers in the park, such as poisonous snakes (and constrictors) and those blasted leeches that WILL try to suck the blood out of you, if you give them the chance!
While Bukit Lawang is famous for its orangutan sanctuary, and Tangkahan is best-known for its elephant safaris, Ketambe is arguably best choice for jungle trekking in the whole of Gunung Leuser National Park. Of course, jungle treks of many days/nights can be arranged from the other towns, but the Ketambe has the infrastructure and the reputation to give you everything you need if you fancy a foray into the rainforest and experience an overnight stay. A lot of the park is incredibly hilly, and broken limbs among hikers is not unheard of as they failed to negotiate the rugged and slippery terrain. Your guide will be able to assess your health and requirements before you set off on the trek, and he can tailor it to best suit your needs.