How do I design a database for continents, countries, regions, cities and POIs?
i suggest 2 options 

Option 1: if you want a RBDMs, i think 2 tables will be sufficient 

Table 1 (Lookup)
-LocationID
-Continent
-country
-region
-City
-Landmark (granularity)


in this Table since its a lookup so i suggest keeping it Denormalized, it will save you alot in your coding specially when joining tables and searching and reporting. and maintenance is  easier, then 5 separate tables

the other table is the table to collect the data

Table 2 (Master)
-Tourist
-LocationID
-ExtraFields
-...


so in this table you collect info about tourists and all you have to do is store the locationid, which is your granularity, this way the Locationid, has the Landmark,city,region,country,continent
Since the Landmark is definetly in a city and the city is in a country and the country is in a region.. (no need for 5 tables to keep them separate, there will be a big chance of invalid inputs or data if not maintained properly)



Option 2:

i suggest graph database, check this post at SO , about using Neo4J for GIS and an implementation of GIS by Neo4J