In this June 14 file photo, hikers and journalists walk along the DMZ Peace Trail in the demilitarized zone in Goseong, South Korea. Eyeing a history-making photo opportunity, U.S. President Donald Trump has issued a Twitter invitation to North Korean leader Kim Jong-un to join him for a hand shake during a visit by Trump to the demilitarized zone. AP

Donald Trump and Kim Jong Un could shake hands in the Demilitarized Zone that divides the Korean peninsula on Sunday if the North's leader takes up the US president's surprise offer to meet.

Trump was to visit the DMZ ― widely referred to as the world's last remaining Cold War frontier ― with South Korean President Moon Jae-in, a day after extending his invitation to Kim on Twitter.

Here are some questions and answers about the Demilitarized Zone, which is based on the positions held at the end of the 1950-53 Korean War, where South Korean forces backed by a US-led UN coalition fought to a standstill with North Korean and Chinese troops.

Where is it?

The four-kilometre-wide DMZ runs for 250 kilometres (160 miles) across the Korean peninsula, around 50 kilometres north of Seoul and 200 kilometres south of Pyongyang.

At its centre is the Military Demarcation Line (MDL), where the front line lay when the ceasefire stopping Korean War hostilities was signed in 1953.

Under the agreement both sides agreed to pull back their forces 2,000 metres. To the south, Seoul has established a further buffer zone of varying width where civilian access is restricted.

What is it?

A barrier separating North and South, heavy weaponry is banned from within the DMZ. Patrols are allowed but cannot cross the MDL and no more than 1,000 people from each side are permitted inside the zone at any one time. It is also littered with minefields.

The areas immediately outside it are some of the most highly fortified places on earth, bristling with artillery, military camps, and more minefields.