The September attack was claimed by Somalia's Al-Qaeda-linked Shebab insurgents.
The trial in Nairobi, which opened on January 15, has heard evidence from people who were at the mall when the gunmen launched their attack.
They described how the fighters stormed the crowded, upmarket shopping complex, firing from the hip and hurling grenades.
Today, the court moved to the burnt-out wreckage of the mall.
The four accused -- Adan Mohamed Abidkadir Adan, Mohamed Ahmed Abdi, Liban Abdullah Omar and Hussein Hassan Mustafah -- have all pleaded not guilty to charges of supporting a terrorist group.
The chargesheet gives no details of the nature of their alleged support, but security sources say the prosecution will argue they aided the gunmen, including by organising accommodation.
The trial resumes in court on January 27.
All the gunmen in the Westgate siege -- understood to have totalled four, not the dozen that security forces initially reported -- are believed to have died during the attack, according to the US Federal Bureau of Investigation.
Somalia's Islamist Shebab said the gunmen came from a special suicide commando brigade.
They said the attack was a warning to Kenya to pull its troops out of southern Somalia, where they are fighting the Shebab as part of an African Union force.
Bodies were buried under tonnes of rubble after part of the mall's roof collapsed at the end of the raid following an intense fire.
