Suggestion on a country

I could throw a dart at a map as can you, but with a single clue as to what you want to see it would be a wasted dart.

Why Netherlands? And Croatia? Not often bedfellows....

We want to visit a place that offers natural beauty as well as nightlife.

If you want natural beauty and for it to be a neighboring country, I would explore Slovenia. The Julian Alps are jagged and beautiful. Lake Bled is lovely and a nice bike ride around the lake. Ljubljana was a fun city with a river that runs through it. The food was very good and the architecture was influenced by the Austro-Hungarian empire. When we were there the European Basketball Championship was taking place. Big screens were set up in various public areas as well as games taking place at an arena. The city was very lively at that time.

NAtural beauty of Netherlands is quite limited. Flat. Quite flat.

But you'll have to admit that Amsterdam does not lack for nightlife. They can get their fill of natural beauty in Croatia, I guess.

OP, you need to be more specific about what you want to do or see. Also, would these extra days be between Croatia and the NL, or after? I completely agree with the comments about Slovenia. Beautiful, with lovely, friendly people.

How many days have you allocated for the Netherlands and Croatia? More than 5 days each, I hope.

How will you travel from the Netherlands to Croatia? By plane, I hope. As you'll be flying, I'd suggest a location with good airport connections - something like Barcelona.

Even flat...I found Amsterdam to be very scenic. North of the city in the less dense areas was more "natural" but then again, everything you see including the land is man made. If you like Techno music there is plenty of nightlife.

"Nightlife"...?? Is that drinking and dancing in a nightclub/bar, or like taking an evening stroll in Rome ( La Passeggiata)?

Netherlands? And Croatia? Not often bedfellows....

Yeah, that sure is a surprising combination. And I must admit that the reason given somehow still doesn't seem like an obvious explanation for this combination of countries.

We want to visit a place that offers natural beauty as well as
nightlife.

Can you be more specific? Do you wish to find those two things in ONE place? Or natural beauty first, nightlife somewhere else? And what is your idea of "nightlife"?

On a side note, I don't agree that the Netherlands does not offer natural beauty. It has a great coastline and some lovely islands for instance. That said, it's not a spectacular kind of natural beauty, and for someone visiting Europe for the first time (as I assume), it's probably not what you are looking for.

You can visit Denmark or Sweden also, they are close to Netherlands, and both have unique culture. There are a lot of monuments and attractions to visit. If you are an art lover then you can find modern art galleries, and various original sculptures. And most importantly you can taste amazing food in diferent interesting cafes and restaurants.

I suggest something close to where you are visiting. Bruges and Ghent, Belgium are worth visit, you could continue on to Paris.

Venice might work out well for you as well.

You can visit Denmark or Sweden also, they are close to Netherlands

What do you consider "close"? Please check your map before saying something like this.

Kopenhagen is about as far from Amsterdam as Prague.

And Stockholm is farther from Amsterdam than Zagreb, and, to make matters worse, in a completely different direction.

Sure, it all depends on your point of reference. If you look at it from Mars, Honolulu is close too.