For a 24-hour visit, a weekend or longer, Michelin Green Guide Short Stays Budapest is your best bet. Michelin rates all sights and activities, grouped by location, with its time-honoured star-rating system and suggests great places to eat and stay.
Travelers will experience the best the area has to offer, whether visiting historic houses, exploring a 9th-century Chain Bridge connecting the hilly Buda district with flat Pest. To riding a funicular railway up Castle Hill to Budas Old Town, where the Budapest History Museum traces city life from Roman times onward. Explore Trinity Square which is home to the 13th-century Matthias Church and the turrets of the Fishermens Bastion, where here you can see sweeping views of the city
This Short Stay guide to Budapest has it all.