Volunteering is an activity that can cause immigration problems for volunteers including deportation. The main visitor  permits are:

• waiver of visa visa (received on arrival, free, at the airport) - allowed activities include 'social', 'tourist', 'business' etc.
• visa-on-arrival (paid on arrival at the airport at the cost of 500,000rp) - allowed activities include 'social', 'tourist', 'business' etc.
• visit visa in advance (paid abroad at the cost of around $50) without a sponsor - for tourist purposes only
• visit visa in advance (paid abroad at the cost of around $50) with a sponsor letter - purpose should be specified, e.g., 'family', 'social', 'business.

Essentially Indonesian immigration have complete discretion to remove any foreigner from Indonesia 'administratively'. The two main provisions are 'misuse' of a stay permit, and 'causing disorder'. Both of these can be interpreted widely. 

Indonesian immigration have suggested  that for volunteers, the volunteer should have a 'visit visa for social purposes', which has been sponsored (with an accompanying letter) by a registered Indonesian yayasan (charity/foundation) and during the application, the sponsorship letter must state that the foreigner is performing volunteer work for the foundation. 

Meanwhile to become an Indonesian resident you can get:

• ITAS - sponsored by a charity or employer. This costs around $1400 per year (including the employer's permit and the cost of the ITAS) and is valid for paid work of the specified nature at the specified employer only.
• ITAS - for investment. This costs around $200 a year, but you must also invest 1 billion rupiah ($70,000) in a special 'PT PMA', and the PT PMA is supposed to be worth over 10 billion rupiah within a year. This allows you to be director of that company and to live in Indonesia
• ITAS - sponsored by your Indonesian spouse. This costs around $200/year and allows you to work in your Indonesian spouse's business, but not in the formal sector.

There have been immigration raids on volunteers in Bukit Lawang, as you can see here. Medan immigration there stated that they do not consider that it is appropriate for volunteers to use the visa waiver facility, and that volunteer work is not allowed in this case. They have wide discretion to make this statement on the basis of 'stay permit' misuse and/or 'causing public disorder', so if you plan to do volunteer work then you should make sure that it is for a registered yayasan who is able to send the formal letter to the Indonesian embassy where you live/online, in order to formally invite you to Indonesia to perform volunteer work.

Voluntourism is big business around the globe. In Indonesia specific considerations are:

• low cost of labour - the minimum wage is around $5/day, and many earn even less. If you emphasise the 'tourism' aspect of voluntourism, then it may make sense to spend thousands on your trip, but the 'volunteer' element may be lacking.
• your skills - if you are a young person with no work or life experience unfortunately you may have little to offer except your time. Effective volunteers will have specific skills that are relevant and scarce in a rural developing area.
• culture differences - Indonesian culture is very different from your own. Communities are interconnected and foreigners are 'other'. You will also face a language barrier - while those working in tourism will speak English, these are certainly not the people in need of help - those in need are generally far from the tourist areas.
• transparency - Indonesia does not have a big charity culture; rather, charity is said to begin at home, and the concept of working for free is largely alien. You should therefore check exactly how the goals of the charity or project organiser himself are aligned with those of the charity. Do not be afraid to ask questions. Indonesian staff need money, but they must explain to volunteers exactly how they benefit financially from their charity.
• safeguarding - Indonesia and other developing countries are open and have few safeguarding policies in place. This means that children can be at risk. If your project is working with children be sure to check about their safeguarding policies
• effectiveness - be sure that your project is effective in achieving its and your goals. Ask specific questions and look at how results are measured. 
• immigration concerns - your volunteer work is likely to be illegal - see above.

You or your project may be unwilling or unable to address these concerns, and this is not necessarily a barrier to you taking part, but you should at least do so with full awareness.

There are many Westerners married to people from Bukit Lawang. In most cases the Indonesian people are former guides.

In the event of marriage, it is normal in Indonesia to have a large wedding party for many people in the village. Attendance may number in the hundreds. The cost of such a wedding is variable, but generally you will buy one cow (sometimes two - costing 10 million rupiah each), plus other food and entertainment. The total cost for such a wedding may be around 30 million rupiah.

The wedding party is separate from the legal marriage, which under Indonesian law must be between two people of the same religion. This means the Westerner, to perform a legal marriage in Indonesia may be required to (at least nominally) convert to Islam. To avoid this, a wedding performed outside Indonesia (which in Western countries does not require you to change religion) is also valid in Indonesia, but the marriage must be reported to the Indonesian authorities within six months of marriage.

Children of the marriage are entitled to dual citizenship, however on becoming an adult they must choose between Indonesian and foreign citizenship - dual citizenship in Indonesia is otherwise not permitted, and those taking a foreign nationality automatically lose their Indonesian nationality.

After marrying an Indonesian citizen you acquire rights to live and work in Indonesia. In particular, your spouse can sponsor a KITAS, or temporary stay permit. This entitles you stay in Indonesia for a year. A KITAS can be converted into a KITAP, or permanent stay permit, entitling a stay of five years. A KITAS/KITAP is accompanied by an IMK, or re-entry permit, which allows you to re-enter Indonesia without losing your KITAS or KITAP. A KITAS IMK has the same validity as the KITAS (1 year), and a KITAP IMK lasts for two years. Work on a spouse KITAS or KITAP is only for your own business - you cannot work for others without a work permit. A KITAS costs 800,000 rupiah, plus 1 million for the 1 year IMK. A KITAP costs 3.5 million, plus 1.75 million for the 2 year IMK.

Westerners cannot own land or property in Indonesia. Land must be owned by an Indonesian citizen. If you wish to buy land in Bukit Lawang you should be married to an Indonesian citizen, who can hold it in their name. A prenuptial agreement may also be required as marital wealth is generally held in common in Indonesian, which is not possible if the spouse is foreign.

Buying land in the name of a third party is a fool's enterprise and heartbreak is essentially guaranteed.

Much of the land in Bukit Lawang belongs to the government plantation company (PTPN) and therefore there is officially no 'hak milk' (ownership right). However, such land is commonly bought and sold by means of a simple receipt between private individuals. This land is not secure and the government could repossess it.

Land which has 'hak milik' should be measured properly and fully certificated (missing certificates could be a sign that the land is mortgaged and in this case you will find the bank will repossess your land leaving you with nothing). Note that it is common for land to be measured 'on the ground', which can mean you get less land than you think, as unless the land is 100% flat, the GPS distance will be less than the distance on the ground. It should always be specified the measurement technique. Hak milik land is subject to a purchase tax of 5%, however it is routine (but illegal) to understate the purchase cost to reduce this tax.

It is possible to rent property in Bukit Lawang for low cost. There are plenty of empty properties and cost is from around 2 million rupiah per year, but this will depend on the building. There is a high rate of burglary from private dwellings and security should always be considered. 

It is common for Westerners to build homes or guesthouses around Bukit Lawang. Local standards of construction are very poor, and available building materials are basic. Better materials can be found in Medan but local builders generally do not have experience of how to use them. Correct building standards and techniques are generally not followed.