Wallenberg was captured by the Soviet Authorities in 1945, detained and then disappeared. There is some question about when his death was but reports suggested that it was more than 2 years later in 1947.
Raoul Wallenberg has received multiple humanitarian honours since his presumed death.
This memorial has some detail about his amazing feat to save so many lives.
The cache you are looking for is a small magnetic film pot, it is not attached to the memorial.
You will need your own pen