Absolutely, I'd be happy to advise you on your trip to Roskilde, Ribe, and Aalborg in Denmark. Below are some travel tips:

Best Time to Visit:
The best time to visit Denmark is typically from May to August when the weather is warmest. However, if you love Christmas markets, December is also a good time to visit.

Route and Accessibility:
You can visit these cities by train or by road from Copenhagen. Frequent public transport is also available. Denmark has excellent biking routes; you could consider cycling between destinations if you're up for an adventure.

Altitude and Acclimatization:
Denmark, being a relatively flat country, won't require any altitude acclimatization.

Accommodation and Booking:
It's advisable to book your accommodation in advance. You can find a variety of options from budget to luxury.

Clothing and Essentials:
Pack comfortable shoes for walking and a rain jacket or umbrella, as rain is frequent. Don't forget a power adapter for your electronics.

Health and Safety:
Denmark is a safe country but maintain general safety precautions. Always have travel insurance.

Local Etiquette and Respect:
Danes appreciate punctuality, calm demeanor, and politeness. English is widely spoken in Denmark, but learning a few phrases in Danish can be appreciated by locals.
In Ribe, visit the Ribe Cathedral and Viking Center. Don't miss Roskilde's Viking Ship Museum and the famous Roskilde Cathedral. Aalborg has a vibrant waterfront, the Aalborg Castle and Aalborg Zoo. Be sure to check their opening hours and any required reservation policies in advance. Enjoy your trip!