Citizens of the UK, Ireland, Australia, New Zealand, Canada and the USA are all allowed to enter the country for thirty days without a visa , while nationals of all EU countries (the UK and Ireland excepted) can remain in Bulgaria visa-free for ninety days. Once this period expires, you either have to leave Bulgaria, or apply for an extension visa at the local police station ( politseiski uchastak , or Ministerstvo na vatreshni raboti - MVR, The latter process involves lots of queuing, paperwork, misunderstandings (people in police stations rarely speak English) and a US$50 dollar fee. It's much easier to head for the nearest border post, leave Bulgaria for a few seconds (making sure that your passport is date-stamped on the way out) and walk back across the frontier again, thereby qualifying for another thirty or ninety days. Border guards are so used to seeing foreigners do this that they're unlikely to bat an eyelid.

If you need further advice, contact your embassy ( posolstvo ) in Sofia.