Getting in is simple as most visitors can enter without a visa for six months, as with the rest of the UK. This includes citizens of the US, Canada, Australia, New Zealand, and the rest of the EU (indefinitely). Always check your passport is good for six months beyond date of return—wherever you travel—and that you have a return ticket to satisfy immigration officials should they inquire.
Health and Safety
Northern Ireland is one of the cleanest and safest travel destinations in all of Europe. Hospitals, clinics, and doctors are decent and pharmacies are common and stock generic and brand name medicines. There are no exotic diseases here and no need for elaborate vaccinations before entry. You can drink the tap water (it tastes better than bottled water) and eateries are monitored for hygiene.
EU visitors can receive emergency medical treatment free of charge with an EHIC card, although everyone should seek travel insurance before departure. There are no major safety risks—The Troubles were over years ago—although keeping away from nationalist/loyalist parades in Belfast and other towns is recommended as trouble can flare up.
Other than alcohol-induced brawls on a Friday and Saturday night, problems are scarce and crime rates here are actually very low. Avoid getting into political discussions in bars—particularly at border towns—and also mind out for pickpockets on public transport and busy streets. The Northern Irish tend to be somewhat erratic behind the wheel, so drive defensively and try to keep downtown Belfast driving to a minimum.