Sure, exploring Fremantle and Rottnest Island will be an exciting tour! Here are some travel tips to keep in mind:

Best Time to Visit:
The best time to visit Fremantle and Rottnest Island is between November and March, during the Australian summer months. However, these months can get quite hot; if you prefer milder weather, April - October can also be a great time, just be prepared for some occasional rain showers.

Route and Accessibility:
Fremantle can be easily reached by train from Perth (about a 30-minute ride). To get to Rottnest Island, you can take a ferry from Fremantle which takes about 25 minutes. Ferry tickets can get sold out in advance during peak times so booking beforehand is advised.

Altitude and Acclimatization:
The elevation of these locations is not high which makes acclimatizing to altitude not a concern here.

Accommodation and Booking:
Both Fremantle and Rottnest Island offer various accommodations ranging from hotels to budget hostels. It is wise to book in advance especially during peak seasons to ensure availability.

Clothing and Essentials:
Pack light, comfortable clothing, and also include swimwear, a hat, sunscreen, and sunglasses for beach activities at Rottnest Island. A reusable water bottle is recommended to stay hydrated throughout the day.

Health and Safety:
It's essential to wear sunscreen due to the strong sun in Australia. If you're cycling on Rottnest Island, remember to wear a helmet and follow the road rules.

Local Etiquette and Respect:
Australians are generally relaxed and informal. However, it's important to remember to respect local customs and ecological preservation efforts, particularly when interacting with wildlife on Rottnest Island, like the famous quokkas.