Visiting the Opera House for a nice concert is a great romantic thing in Budapest whether you love operas and classical music, or just bear them. It is a nice place, the opera tickets range from very cheap ones to more expensive entries, but the performances are high quality.
The neighborhood of the Budapest Opera House provides a nice setting for a night walk.
Along Andrassy Avenue, you can head to Liszt Ferenc Square to sit in one of the dozens of terraced cafes and restaurants, or you can walk towards Deak Square past the high end fashion stores with dazzling minimalist but luxurious windows.
Why not hop in for a minute to take a look around (unless your better half hates shopping, that is)? Some of the luxury shop displays in Budapest are truly amazing.
Andrassy Avenue is flanked by trees, restaurants, historical buildings, villas and embassies, old residential buildings with fascinating staircases, and over a hundred year old courtyards, beautiful Atlas figures at the entrances, and some of the best shops in Budapest all along, which makes it a pleasant place to walk, or sit out to people watch.