Oscar Pistorius sits in court during proceedings at the North Gauteng High Court in Pretoria, March 19, 2014.

From worries about what Russia's Victory Day could mean for Ukraine to the latest challenge for the "vertical running" set, here's a look at some of the most interesting stories coming up around the world this week.

Oscar Pistorius Murder Trial Goes Back to Court

Oscar Pistorius returns to the dock Monday as his trial resumes in Pretoria. The court adjourned last month after 25 days of dramatic testimony. As many as 11 additional witnesses are expected to be called during the next two weeks of testimony. Defense sources tell ABC a ballistics expert will be among those witnesses to back up Pistorius' version of how he shot his girlfriend, Reeva Steenkamp, on Valentine's Day 2013. Pistorius is said to have spent the past three weeks recuperating and resting from after a five-day verbal mauling in court by the prosecutor Gerrie Nel - known as the "Bull Terrier." Pistorius faces 25 years to life in prison if convicted of premeditated murder, but it could be some months yet before he - and we - learn his fate.

Mandela's Party Faces Toughest Challenge in South African Election

South Africa's President Jacob Zuma will learn what his future holds rather sooner. Twenty years after Nelson Mandela won the country's first post-apartheid election, South Africa goes to the polls on Wednesday, with Mandela's party, the ANC, facing the biggest threat to its rule in two decades. Zuma is beset, not just by huge economic and social challenges, but is fighting to clear his name. South Africa's public prosecutor says the president misappropriated more than $20 million to upgrade his private home, including a pool and a cattle enclosure paid for by taxpayers. The prosecutor accuses Zuma of unethical conduct. The ANC has won two-thirds of the vote ever since white-majority rule ended. But Zuma, long controversial, is now accused of being venal. Opposition parties have promised to vote against him as president - even if the ANC wins a majority in Parliament. And if the ANC wins less than 60 percent of the vote, the biggest threat to his leadership could come from within his own party, rather than outside.

Russia Celebrates Victory Day

Friday is one of the biggest days of the year in Russia. Victory Day commemorates the Soviet victory over Nazi forces during World War II. Every year the public holiday culminates with a huge parade in Moscow's Red Square, showcasing Russia's military might. WWII is known in Russia as "The Great Patriotic War," and this year - amid the crisis in Ukraine - there could be a second act to Victory Day. Russian media reports Vladimir Putin could spend the holiday in Crimea - just a month after Russia annexed the peninsula. This year marks the 70th anniversary of Crimea's liberation from Nazi troops. The Russian newspaper Kommersant says after the parade in Moscow, Putin may fly to Crimea's capital, Sevastopol, to take part in festivities there. Ukraine also marks Victory Day with a public holiday. But many, particularly in western Ukraine, believe that the country fought a war on two fronts between 1939 and 1945 - one against Soviet occupation and one against the Nazi advance - leading Ukraine's interim prime minister to warn that the anniversary means the country is entering its "most dangerous 10 days" since independence in 1991.

Jailed Journalists to Be Honored on World Press Freedom Day

The UN proclaimed May 3 World Press Freedom Day 21 years ago. Some 1054 journalists have died doing their job since 1992, and 14 have been killed so far this year alone. To mark World Press Freedom Day, the three Al Jazeera journalists jailed in Egypt have sent open letters expressing their gratitude for the continuous support by all calling for their release. Saturday marks the 126th day they've been held - and once again, they'll be back in court. The former BBC reporter Peter Greste, who is imprisoned in Cairo's notorious Tora prison, hailed the fact that "press freedom is being vigorously defended, and in a way that would have been unimaginable before our arrest." Earlier this week the UN Secretary General Ban Ki-moon, raised his concerns about the detention of the journalists during a meeting with Egypt's foreign minister.

'Vertical Running' World Series

And it's not just baseball that has the World Series - so too does what's called "vertical running." If you think the stepper in the gym is hard work, spare a thought for the world's "skyrunners." The world's most iconic skyscrapers are the stage - the sports' biggest stars can race up 100 flights of stairs in just a handful of minutes. And after kicking off with the Empire State Building in February, this weekend, the "Vertical World Circuit" rolls into Taiwan, and one of the world's tallest buildings - the Taipei 101. It stands 1,600 feet high. The runners will climb 1,300 feet, over 91 floors. And if that wasn't enough, they have to beat an astonishing record of 10 minutes, 29 seconds, set by Australian runner Paul Crake in 2005.