Many people can visit New Zealand without a visa. A visitor’s permit is issued at the airport, typically for three months, although British citizens get six months.
You can check the countries the visitor’s permit applies to on the NZ Immigration website.
If you want to stay longer than permit will allow, either apply for an extension once you’re in the country or get a visa before you travel.
The problem with applying for an extension in NZ is that you need to show an onward ticket to get into NZ in the first place and if it’s dated beyond your first 3-month allowance, this could cause a problem. Applying for an extension will also take up some of your holiday time.
On the other hand, getting a visa is expensive and time consuming. The visa fee is about $100 U.S. and on top of that you will have to pay for a bank draft and you may need to get copies of your passport certified. If you are applying while on the road, your application may need to be sent to the NZ embassy in your home country.
You could also need chest xrays or a medical checkup, although this is unlikely.