Sure, here are some travel tips for your visit to Copenhagen, Hillerød, and Helsingør in Denmark:

Best Time to Visit:
The best time to visit these Danish cities is from early summer (May to June) till early autumn (September). During this period, the weather is pleasant, and you can enjoy long daylight hours.

Route and Accessibility:
From Copenhagen, you can easily reach Hillerød by train in approximately 45 minutes. From Hillerød, Helsingør is within an hour's distance by train. Public transport is efficient, punctual, and reliable in Denmark.

Altitude and Acclimatization:
These cities are at sea level, so altitude acclimatization is not a concern.

Accommodation and Booking:
Copenhagen has a wide variety of accommodations to fit different budgets. Hillerød and Helsingør, being smaller towns, offer fewer options but you should find something comfortable. Book in advance, especially if your visit coincides with the tourist season.

Clothing and Essentials:
Pack for cool and potentially rainy weather, even in summer. Comfortable walking shoes are a must for exploring the cities. Don’t forget an umbrella or raincoat, and sunscreen for the sunny days.

Health and Safety:
Danish cities are generally safe. However, always keep an eye on your belongings, especially in crowded places. If you have specific health concerns, carry necessary medicines.

Local Etiquette and Respect:
Danes usually expect people to respect personal space and be punctual. When visiting churches or other places of worship, dress respectfully. Denmark is also known for its sustainability practices, so try to limit your environmental impact by recycling and avoiding litter.