Most of the visitors to Northern Cyprus do not need to obtain a visa in advance for short visits.
Citizens of all countries may enter without a visa for up to 90 days except for the citizens of the following countries:
They must obtain a visa at one of the diplomatic missions of Northern Cyprus.
Nationals of Bangladesh are refused entry to Northern Cyprus by air (it is unclear whether this also applies to sea and land entries) 
Visa on arrival was issued when crossing from the Republic of Cyprus until May 2015.
Visitors given less than 90 days on entry but wishing to stay longer (up to 90 days) can apply for extension at the Immigration Department of the Police Headquarters. To stay longer than 90 days, they have to exit and re-enter the country. Overstayers will be issued a visa penalty fine (100.23 Turkish lira for each day) that has to be paid on a future re-entry.
For visits of up to 90 days (i.e. without obtaining a work or residence permit), citizens of
may enter the TRNC using national ID cards (incl Irish passport card) instead of a passport.