Every-year Thailand [object-を] visit European-people's number very many.
Note the missing が or は — 数とても多い drops the topic marker (a casual omission). 訪問する ('to visit') is the formal counterpart of 訪ねる — more common in news and formal contexts. Relative clause 訪問するヨーロッパ人 modifies 数 ('the number of').