Of course! Kyoto, Nara, and Koyasan are some of Japan's most historic and interesting destinations.

Best Time to Visit:
You can visit these places year-round, but April-May and October-November are particularly beautiful due to the cherry blossoms and autumn colors respectively. However, please avoid Golden Week (end of April to early May) as it can be quite crowded.

Route and Accessibility:
All cities are well-connected by Japan's rail network. From Osaka, you can reach Kyoto and Nara by JR lines, and Koyasan by the Nankai Line. Japan's efficient public transportation makes it very accessible, so consider getting a Japan Rail Pass for unlimited travel.

Altitude and Acclimatization:
These regions are located at a comfortable altitude so acclimatization isn't typically a concern you need to worry about.

Accommodation and Booking:
You will find a wide range of accommodation options in each city, including traditional ryokans (Japanese-style inns). It's recommended to book in advance especially during peak seasons.

Clothing and Essentials:
Depending on the time of year, dress in light layers during spring and fall and warmer layers in winter. Summer can be quite hot and humid. Also, remember to bring comfortable walking shoes as you will do a lot of walking and possibly hiking in Koyasan.

Health and Safety:
Japan is generally safe and clean. Still ensure that you have international travel insurance and follow local regulations and advisories, especially those related to COVID-19.

Local Etiquette and Respect:
Be mindful and respectful towards local customs. Silence is greatly appreciated in temples, shrines, and public transport. Tipping is not standard in Japan. Also, it's customary to remove your shoes when entering traditional Japanese inns, temples, and sometimes restaurants.