We planned to use our long layover to explore a new city. It completely backfired, but we'd try it again.

• As an American, I didn't realize I needed a visa to leave Istanbul's airport during my long layover.
• The oversight cost me more time, money, and stress than anticipated.
• Now I know that researching country-specific entry and visa rules can prevent costly mistakes.

My fiancé and I have a knack for piecing together budget-friendly flights, and last August, we put our skills to the test to attend a wedding in Crete.

To save a few hundred bucks on our trip out of New York, we booked a flight that included a 13-hour layover in Istanbul and a brief stop in Athens.

Many people in our lives thought stopping for over half a day in one place sounded miserable, but we had a plan: We'd maximize our layover and use it as a chance to explore a new city and visit an old friend.

However, shortly after we arrived in Istanbul, things took an unexpected turn.

Unfortunately, our layover didn't go as planned

My friend wasn't feeling well, so we scratched our plans to meet her in the city center.

We weren't worried because we could still explore Istanbul on our own — and we decided to take advantage of Turkish Airlines' free city tour for layovers.

When we arrived at the tour desk, though, we learned that Americans need a transit visa if they want to exit the airport in Turkey. We had no idea and hadn't made any arrangements in advance.

We're usually very careful about checking travel guidelines and regulations — and I couldn't believe such a seemingly small oversight would change our plans entirely.

Although we could've tried applying for emergency visas, doing so would've cost us a lot more than we'd budgeted for our brief layover.

So, we now had 13 hours to kill without leaving the airport.

We made the most of being stuck, and I learned a valuable travel lesson

We tried to make the most of spending hours upon hours walking around the Istanbul Airport, which is actually quite beautiful.

As an interior designer, I genuinely enjoyed taking in the architecture and design details of the modern and elegant space. We also ended up shopping and buying overpriced airport food.

Between meals, drinks, souvenirs, and my fiancé's spontaneous purchase of a drone, our layover costs quickly added up.

Unfortunately, in a few hours, we'd basically spent the amount of money we'd saved by booking a flight with layovers instead of a nonstop one.

The next leg of the journey wasn't without its own set of hurdles either. When we finally reached Athens, my luggage broke as we stepped off the plane.

After 24 hours of no sleep, multiple layovers, and unexpected expenses, we were exhausted when we got to Crete.

However, even with these mishaps, our Istanbul layover was a unique experience that I wouldn't write off completely — though we'd definitely be better prepared next time.

The biggest lesson we learned is that it's crucial to double-check each country's entry requirements before assuming we can explore a new place during a layover.

And, if you need a visa to exit an airport, apply for it online before the trip to save both time and money.