For non-Xiamen residents, getting to the historic island of Gulanyu is cumbersome. They need to board ferries leaving from the International Cruise Center at Dongdu, which is next to Cruise Center station on Line 2 (green).
Pre-booking for weekends and public holidays is essential as there are many tour groups and ferries fill up quickly. Chinese residents can book it on their mobile phones but I was told by my hotel concierge I need a local phone number to receive the booking SMS. So if you are a foreign tourist without a local number, you will need to physically go to the terminal to book.
When I arrived at lunch time on a Sunday, the next regular ferry available was 2.5 hours away at 3:30pm. There are other more expensive options leaving earlier including an island cruise + landing for over CNY 200. I paid CNY 60 for a "luxury" ferry to Sanqiutian port, which is closer to the historic centre on Gulangyu.
At the manual counter, there are signs that the last ferry back to the International Cruise Center is at 5:40pm. I asked a couple of staff about this and they told me that's because the cruise terminal closes then, but doesn't mean you need to vacate the island by that time or risk being stuck there overnight.
This ferry has 2 stories and there is an open deck at the back of the top floor. The journey takes about 20 minutes with good views of the city on the left side.
Xiamen residents, on the other hand, get to use the city centre ferry terminal to reach Gulangyu, a much shorter 5 minute ride and you can see the other side easily from the port.
More : https://globalphotos.org/xiamen.htm