Brussels was the capital city of Belgium, and a place that the Doctor visited on several occasions.
In 1913, Brussels was the scene of the final confrontation between Toby the Sapient Pig and his creator. (AUDIO: Year of the Pig)
Several decades after this, Haresh and Gita Chandra had their honeymoon in Brussels, which Gita did not enjoy. (TV: The Wedding of Sarah Jane Smith)
In 2001, the Eighth Doctor reunited with Fitz Kreiner in the city, after a long period of absence from each other. There, they chanced upon Anji Kapoor and her boyfriend Dave Young, who were on a holiday which they hoped would rekindle their romance. Instead, they became embroiled in the Doctor's effort to prevent the Kulan invasion of Earth — during which Dave died and an emotionally devastated Anji became a companion of the Doctor. (PROSE: Escape Velocity)