If most of people here in Slovakia knew english, I'd invite you here.
Technically you could visit northern Slovakia (which borders with Poland), but other than that, it would be probably problematic to communicate (judging by myself, because I don't know polish, maybe except a few words).

You should invade you neighbor Lithuania! I Spent a while in Vilnius and it was fantastic! It has all the features I look for in a victim nation, cheap and delicious beer, ridiculously cheap food that has more cream than I thought possible. I was surprised by how friendly and outgoing the people there were. It's also the cheapest European nation I have ever visited which has to count for something.

I'll thank you not to give out disinformation. Denmark does NOT use Euros. Same situation here as in Sweden. We have our own currency, but you can pay with Euros in some places. It's a tourism thing.

Oops, sorry.

From the named countries I only visited Czech.
It's a great country, beautiful women and home of Pilsener.
Not mentioned here is Hungary.
Budapest is great in the summer, especially around and during the Sziget Festival.
No idea if it's an upside or downside for you, but there were quite some Polish people there this year.
If you like beers, Belgium is a good place.
Go to Gent or Brugge.
Portugal, Spain, France, Italy and eastern European countries can be problematic sometimes as people there don't speak much English, or sometimes simply refuse to speak it.
Scotland (British pounds) and Ireland (Euros) are great in August.
Both have beautiful landscapes, friendly people and great whisk(e)y.
Personally I prefer Scotland over Ireland though.
Germany always give me a bit a been there, done that feeling.

Where can you see lions? Only in Kenya
Come to Kenya we've got lions
Where can you see negros? Only in Kenya
Come to Kenya we've got negros
Forget Norway
Kenya, oh Kenya
Where the Giraffes are and the Zebra
Kenya, Kenya, Kenya, Kenya
Kenya, going to Kenya

I think my friend from Nigeria would find that racist if I sang that to him with a group of band geeks...Funny as hell though since he has been there.