Answer:
1. Los turistas ya habían perdido sus pasaportes cuando llegaron al hotel.
<em>The tourists had already lost their passports when they arrived at the hotel.
</em>
This sentence is an example of the <u>Past Perfect</u> tense.
2. Paula decidió alojarse en un albergue, pero aún no sabe en cuál.
<em>Paula decided to stay in a hostel, but she still doesn't know which.</em>
This sentence is in the <u>Preterite</u> tense.
3. Mateo había reservado el hotel desde hacía cuatro meses.
<em>Mateo had booked the hotel four months ago.</em>
This sentence is also in the <u>Past Perfect</u> tense.
4. Se hace tarde y nosotros aún no terminamos de hacer las maletas.
<em>It's getting late and we haven't finished packing yet.
</em>
Another example of the <u>Preterite</u> tense.
<em />
5. Hoy ellos recorrieron el centro histórico de la ciudad.
<em>Today they toured the historic center of the city.
</em>
This sentence is also a the <u>Preterite</u> one.
<em />
6. ¡Nunca antes había estado en un crucero! ¡Lo disfruté mucho!
<em>I had never been on a cruise before! I enjoyed it a lot!</em>
This last sentence is in the <u>Past Perfect</u> form.