Tobor The Great

At his underground laboratory in Los Angeles, Professor Nordstrom (Taylor Holmes), worried that manned space exploration is too dangerous, enlists the help of Dr. Ralph Harrison (Charles Drake), who recently left the new government-appointed Civil Interplanetary Flight Commission. The two scientists embark on a research project to create a robot that can replace a human for space flight. Nordstrom's daughter, Janice Roberts (Karin Booth), and her 11-year-old son Brian (Billy Chapin), nicknamed âGadgeâ, become very interested in the project.
When a press conference is called to announce the creation of "Tobor", reporters, such as the inquisitive journalist Gilligan (Alan Reynolds), are invited to Professor's Harrison's home to see the remarkable invention. In order to undertake space travel, the remote-controlled robot has been given some human capabilities, including the ability to "feel" emotions and react via a telepathic device built into his robotic brain. Under the watchful eyes of Harrison's trusted assistant Karl (Franz Roehn), the giant robot Tobor is unveiled and then demonstrated. Unknown to the scientists, a foreign spy chief (Steven Geray) has quietly joined the group of reporters; he quickly draws up a plan to steal the robot.
While trying to perfect the robot's control systems, an inadvertent episode involving Gadge, who sneaks into the laboratory and turns on Tobor, shows that the robot can make emotional connections with people. Gadge not only controls the robot, but when he is accidentally tossed about, Tobor appears to comfort him, as if he is sorry for hurting the boy. After cleaning up, the scientists realize that an additional chair had to be brought to the news conference, leading them to believe that someone has infiltrated the closely guarded laboratory. Aware that their robot could fall into the wrong hands, they construct a small transmitter in a fountain pen that will be able to communicate with Tobor.
When an organized attack by foreign agents is thwarted by the defensive devices at the Nordstrom's home, the spies hit on another scheme. Sending Gadge and his grandfather an invitation to a space flight presentation at the Griffith Park Planetarium, they intend to hold them as hostages when Gadge and Nordstrom show up; the spies are successful and kidnap them. Dr. Gustav (Peter Brocco) tries to force Nordstrom to give them the crucial information needed to control the robot.
When Nordstrom and Gadge do not come back to the laboratory for a demonstration of Tobor to military officials, Dr. Harrsion contacts the local sheriff with his concerns that something dire has happened to them. Suddenly, Tobor is activated, reacting to messages sent by Nordstrom, and storms out of the house, driving off in a military Jeep. The professor is actually controlling the robot with the pen transmitter, all the while trying to fool Dr. Gustav. One of the spies realizes the pen is important and snatches it away, breaking it.
Guessing that the robot is going to rescue the professor and Gadge, Harrison and the military officials follow. At the enemy agents' lair, when the transmissions stop, Tobor comes to an abrupt halt, but Ralph successfully re-activates the robot using telepathic commands. The spies then threaten to hurt Gadge, who instinctively reacts and uses his mind to call out to Tobor to help him. Nordstrom relents, writing out the information. In company with Harrison and the military men, the robot breaks down the lair's door and attacks the enemy agents, rescuing the professor and his grandson. When one of the spies attempts to escape with the coerced information, Tobor yanks him out of his car. Gadge is then gently carried out by Tobor.
Later, when the robot has been successfully reprogrammed, a spacecraft is launched with Tobor at the controls.

Question: where they intend to hold them as hostages?
Answer: Griffith Park Planetarium; Griffith Park Planetarium