Don't worry about "being completely natural". Nobody expects that.
There are no magic words. If you put 20 native speakers of English in the same situation you would get 20 different expressions.
So "Is there a bus that can take me to ..." is completely understandable.
"When is it?" is understandable. If there is more than one bus the person will probably tell you when the next bus is. If you want the last bus of the day then "When is the last bus?" works fine. If you want to know about how often the bus leaves then "How often does the bus leave?"
But it is often easier to find the information since the timetable is printed on the bus stop. It is also usually on the internet, so you can see it with a phone.
Note that train staff don't work for the bus company (in the UK) and so won't know anything about the details of bus timetables. Similarly, you may well find that people in the tourist attraction have no idea about when buses leave.