Ngo Tran Hai An, a travel blogger and photographer, has visited over 100 land and island border markers in Vietnam and around the world for 19 years.

When An visited Con Dao Archipelago in southern Vietnam with his family, he decided to track the A3, A4, and A5 landmarks. These are three of the 11 baseline location points, marking Vietnam's territorial waters, which are located along its 3,260-kilometer coastline. Most of the points are on remote islands and difficult to reach.

An said in 2010, he started off visiting 11 landmarks in 11 years, Con Dao marking 9 out of 11.

His journey started at 6 a.m. from Bay Canh Islet (Hon Bay Canh) where the A5 landmark is located. Of all the islands where the landmarks are situated, this is the only spot that has been tapped by tourism. The remaining landmarks are located in untouched parts of Con Dao, with few canoes or boats going there.

An said one of the challenges was the total lack of information about the location he was heading to, on top of the fact the islands were quite big. Most people refused to take him there since there was no safe place to dock. An eventually received help from Van Hung, an officer of Con Dao District's Department of Culture and Information, who hired a canoe for him.

According to canoe driver Phat's memory, the landmarks are located at the farthest eastern point on the islands.

Rock formations on Bay Canh Islet were the first to catch the visitors’ attention. The road to the landmark features a narrow concrete staircase. The team had to wait for the waves to lift the tip of the canoe higher so An could jump ashore.

An was overwhelmed with the majestic beauty surrounding the landmark. Behind the landmark stands steep cliffs, and a lighthouse further up built in the French colonial era.

Leaving Bay Canh Islet, the group headed to Cau Islet, which does not have any visible A-landmark, though another local milestone helps define Vietnam’s sovereignty. With no road to the landmark, the boat had to dock on the slippery rocks, surrounded by many sharp oysters. An said Cau Islet’s rugged beauty made it his most favorite out of all islands.

Standing next to the landmark, surrounded by a vast sea of water, An felt extremely touched: "This is heaven and earth, the frontier of the country".

The A4 milestone on Bong Lan Islet was the next destination, located about 20 minutes from Cau Islet. The islet was named after a type of vanilla cake called bong lan in Vietnamese. It is very small and home to many swifts. Their nests are created from solidified saliva and considered a delicacy in some countries due to their high nutritional value. Due to their popularity, local authorities have appointed guards to protect the nests from thieves.

Boats often do not reach the shore due to rocky rapids, so the team needed to jump onto the islet. An said visiting milestones is a worthwhile experience, but the journey is difficult and dangerous, so it is reserved for those with a deep drive for exploration.

At Tai Lon Islet, it proved difficult for An to reach the A3 milestone because the road was blocked by iron railings. Besides, a strong wind caused the boat to collide with the rocks, damaging a large part of its hull.

An said he was very impressed with this islet because it is much bigger than Bong Lan. Tai Lon is home to a primeval forest and pristine rocky rapids.

The A3 milestone declares Vietnam’s sovereignty over Tai Lon Islet in Ba Ria – Vung Tau Province.

After visiting the A3 milestone, it started to get cloudy and the wind became stronger. Following canoe driver Phat’s advice, An decided to visit another landmark on Ba Islet, 30 minutes away.

The road to the landmark on Ba Islet is filled with coral reefs. To avoid damaging the corals, An decided to go via shore. The traveler also had to hike for a while before reaching the landmark.

The view from the landmark on Ba Islet shows Love Summit (Dinh Tinh Yeu in Vietnamese), the symbol of Con Dao.

An said the journey to the milestones was strenuous but he left with many memories and feelings, one of them he described as a sense of pride “that is hard to put into words.”

He said that if visitors rent a boat, they should talk with the driver in advance to make sure they take them to the right landmarks because not everyone knows exactly where they are since the islands are usually big.

The cost of renting a canoe is about 260 USD for a 4-hour trip. When you go, you should depart early in the morning when the weather is calm and bring appropriate shoes for the hike. An strongly advises visitors against vandalizing the landmarks and to not take home any object they find here to help preservation efforts.