If you mean “underrated” as not having visitors in numbers a) relative to the native population, b) relative to the number of sites of interest or c) relative to the surface area of the country, it is a question that can be answered in several ways.
Using international arrival statistics won’t provide a neat answer
First of all, within the EU, especially between contiguous countries in Schengen, there is no record of border crossings, far less than by nationality.
Some could be commuters (trans-frontier workers), shopping trips or just transiting.
Even using airport arrivals in a given city doesn’t necessarily reflect the final destination as the international visitor must clear EU Schengen border control in the first port of entry, usually a hub like CDG, FRA, MAD, LON, AMS, ZRH…
If, to focus on tourists from afar, once could restrict to visits arriving by air.
However, that would be falsified by a) business trips (favoring big economic centers), b) relatives (favoring Ireland the UK for many N. Americans) and c) schedule and length of visitors’ holidays (US only give up to 2 weeks per year; EU gives as much as 4 or 5 weeks; so, the US visitors will be very seasonal whereas intra-EU travelers can visit throughout the year.
Using Unesco Sites as a Rough Indicator
Then, how does one calculate the number of tourist attractions that would merit an international visitor and a neighboring country visitor? One can use the very rough indication of the number of Word Heritage Assets. In that case the “most attractive” EU countries would be:
Why do visitors go to a country?
There are many reasons for visitors, some or all of which vary by season and by country, or region of country
Business and Official (Major cities predominate like Paris, London, Frankfurt that are also airline hubs; also locations of major international institutions (Brussels, Paris, London, Geneva, Amsterdam, Viena…)
Family gatherings (A) Trans-European extended families such as Spaniards from Civil War exodus, Poles migrating West, Britons retired in Spain, Romanians migrated West. B) Americans/Canadians with Irish, British, German or Italian family, C) Latin Americans who emigrated to Spain
Daily commute for work. A) Rhine Valley region next to France/Germany border, B) Between Geneva Canton and France, C) Between N. Ireland and Eire etc.
Winter holidays. To France, Switzerland and Austria mainly.
Summer holidays. To the Mediterranean (Spain, France, Italy, Greece)
Cultural Sites. To Italy, Spain, France, Germany, the UK.
Cultural Events. To France, UK etc.
Lower cost. To Portugal, Spain, Bulgaria, Balkans
Good tourism service. To Switzerland, Spain, France…
When is a country “underrated”?
This would be when the number of non-resident hotel nights doesn’t correspond to the number of attractions. Obviously, those countries with the most number of attractions should have the most foreign visitors staying in hotels. So, here are countries with attractions but have fewer than expected tourists for any number of reasons (e.g. inadequate marketing/bad press, under-capitalization, climate, poor tourism infrastructure, difficult logistics, high cost, security…)
Romania. This country has 7 World Heritage Sites but only 760k visitors per Site per year (compared to 9 M per Site in Ireland!). It is far away on the Eastern edge and infrastructure is inadequate over a relatively large land area. There has also been an exodus of youth and educated to the West in search of work. While most know of Bucharest, few have even heard of the appeal of Cluj-Napoca that has charming corners and street life and a burgeoning IT services sector attracting youth and entrepreneurs.
Small, neo-democracies such as Slovakia, Lithuania, Montenegro, Latvia and Estonia may be too recent to have much developed and also may represent less easy logistics.
Scandinavia. Despite their large land area, these countries have small populations, are more expensive to visit and known mainly for cold, long winters. That said, they host only about 1 million tourist nights per World Heritage Site per year. Only Iceland does OK with 2.6 million visitor nights per WH Site per year - perhaps artificially high due to the low cost of a stopover on WOW Air or Icelandair.
Belgium, despite being a logistic surface transport hub and hosting EU and NATO institutions only hosts 1.4 M tourist night per WH Site per year. It has a reputation of having grey weather and flat land, mostly known for diplomats. However, Brussels is only 90 minutes from Paris and is a hub for low cost airlines.
Bulgaria has had the most dramatic youth and brain drain after accession to the EU as the corruption, inefficiency, poor infrastructure and bad economy led many of those who could to emigrate West. It’s population has dropped from 11 M pre-EU to just over 8 M. Entire towns are now populated with more elderly people. It is also the only EU nation that used the Cyrillic alphabet (its invention). It does have among the lowest costs of living in the EU and the Black Sea resorts of Varna and Burgas, the most noteworthy, but they attract lower-spending tourists on package deals from the UK through Russia. Plovdiv has artefacts of ancient civilizations and there is a Mediterranean climate in the southern and eastern zones.
Sam Sure, Mature Bachelor who lived in Europe and the US