Hello! That sounds like an exciting trip you've planned to Marstal, Faaborg, and Copenhagen. Here are some tips tailored specifically for you.

Best Time to Visit:
For the mentioned Danish cities, the best time to visit is from May to September, when the weather is mild and days are longer. The temperatures during this period range from 15 to 25 degrees Celsius, making it perfect for outdoor activities.

Route and Accessibility:
The best way to visit these cities is to fly into Copenhagen, then use the excellent Danish domestic transport system. Marstal and Faaborg can be reached by ferries from Copenhagen, and local buses or bikes can be used for getting around within the cities.

Accommodation and Booking:
All three cities offer a variety of accommodations to choose from including hotels, inns, B&Bs, and homestays. It's best to book in advance, especially during the peak tourist season (June-August). Websites like Booking.com or Airbnb are good platforms for reservation.

Clothing and Essentials:
Pack layers for this trip, as the weather can be quite varied, even during summer. Rain gear is a must as light showers can be quite common. Carry comfortable walking shoes and don't forget essentials like sunscreen.

Health and Safety:
Denmark is generally very safe and has excellent healthcare facilities. It is always advisable to have travel insurance and keep emergency contact numbers handy. For any emergency, you can dial 112 in Denmark.

Local Etiquette and Respect:
Danes appreciate punctuality, respect for personal space, and modesty. Tipping is generally included in the bill, but small additional tips for good service are appreciated.