Madrid
*safety: Locals told me the area around Blaha Lujiza Ter is not the safest. As a group of guys we never had an issue but you might want to keep this in mind when booking.
Restaurants
Riso
A MUST! One of the best Restaurants I have ever been to. Great location, nice and quiet, delicious food and friendly staff. Tipp: get their deserts , they are great (especially everything with rice). For Budapest rather expensive but for around 25-35 euros you can get starters, a main, desert and drinks and it is definitly worth it.
Bestia
Very cool place. They also have seating outside. I recommend the spare ribs or the parm chicken. Also rather expensive but definitly worth it.
Dyonisos Taverna
The inside is beautifully decorated and I would recommend sitting there. For starters definitly get the small fried fishes. Their wine is great too.
Cafés, Bars & Nightlife
Szimpla
Very touristy but I recommend going if you have not yet. Very cool vibe and perfect for some relaxed drinks.
Zsiráf
Great outdoor bar for the evening. The plants and lights give it a really cool atmosphere. There is music as well and the place is really lively. Great to start a night out.
Mika Tivadar Kert
Entrenched between buildings is Mika. A great outdoor bar with a really cool vibe.
Instant-Fogas Complex
The most famous club in Budapest. Not necessarily a must but if you look for the club where all the tourists are, Instant is your choice. They have many rooms for all the different music genres from latino, rock to club bangers. Always a safe bet to have a good night.
Ötkert
Ötkert has a cool vibe with the open air dancefloor. In case it rains they cover it. A bit more relaxed than Instant. Great for dancing.
AETHER Club
Supposably good but have not been.
Activities
Get a buggy and cruise around Sziget-Island
Go to the roundabout a the beginning of the island and rent a buggy. Check out the different rental stations and get the vehicle you want. Some might be more expensive than others. However most of them are cheap. Drive around the island and have fun.
Go to a thermal Spa
The map shows three Spas. Spa 1 is rudas baths which is the only one I have visited but there is no reason to switch since it is great. Inside is very beautiful with the main hall having colored tiles in the ceiling. On the roof is a 360 degree pool (pictured) and there are many saunas and steam rooms. Get the ticket with full access (about 25 euros) and enjoy. Also make sure to check the website beforehand as some timeframes only men or women are allowed (most of the time both tho). The other spas are more famous however, yet also more touristy.
Stroll around Budapest Parc
Just walk around the parc and explore a bit. There are also places to eat or drink inside it.
Watch a waterpolo game
Check the schedule if they play. If they do make sure to attend a game in their gym. It is a bit hidden and there is not really a lot of information (especially none in english as no tourists usually attend). But it is definitly a great experience as waterpolo is very big in hungary.
Go into the Labyrinth of Buda Castle
Always fun is going into the labyrinth. It costs entry and you get a laterna to explore the dark labyrinth.
eat kürtőskalács
Traditional cake which is really famous. There are different places where you can get it. You can often choose from different coatings, like cinammon and sometimes even stuff it with ice cream.
Spots
The fishing bastion
Great hangout spot for the later afternoon. You have a nice view over the city. There are often many tourists here. If you fancy a more quite spot walk a bit more into the town and there is the Pavilon spot.
Top of the Citadella
The walk to the citadella may take you around 20-30 minutes and you may sweat a bit. But it is well worth it as at the top you get the best view over Budapest. And sometimes there are also places to get a strawberry beer or some langos open.
On top of Buda Castle
The walk through Buda Castle is very nice and at the end you also have a great view over the city. Like all the spots they are the most beautiful around sunset.
Pavilon
Just a quick walk from fishing bastion the Pavilon offers a view behind the hill of Buda. Very nice place to hang out and chill.