Debrecen is the "Capital city of the Great Hungarian Plain", and the county seat and largest city of Hajdú-Bihar county in eastern Hungary. It is the second largest city in the country with about 200,000 inhabitants and historically the most important city in Hungarian protestantism.
They used to say "who in their sane mind would build a city in the middle of nowhere where there are no mountains, forests, water or roads?". Still, the answer is a mystery, but Debrecen is the second (or third, depends on the census) largest city of Hungary.
It used to be Europe's largest Calvinist city (was called "The Calvinist Rome"), and the Grand Church (Nagytemplom) is a reminder of the city's heritage.
Debrecen also has a university with all kinds of science areas. It has about 25000 students. The main building at the Nagyerdő is beautiful.
It can be easily accessed from Budapest by driving on the M3 highway and then the M35 (about at 186 km sign) highway but vignette is required. It is about a 2-hour drive. Or follow the main road 4 from Budapest or anywhere except east (more than 3 hours travel from Budapest), but it is not recommended because main road 4 is overcrowded and accidents are common.
There is an airport , but commercial traffic is low. There is a discount airline (Wizz Air) flying from München, Eindhoven and London. It is planned to extend the air traffic through involving more cheap-flight companies. Charter flights come regularly to the airport.
There are trains from Budapest to Debrecen frequently. InterCity trains, the fastest type, takes 2.5 hours to reach Debecen, and also stops at Budapest Airport (Ferihegy station). Cost is HUF 4485 (2nd class) or HUD 5475 (1st class)
Roads are okay. The city is small enough though that you could easily get around by foot or by public transportation.
Public transport uses local tickets. Don't try to use Budapest tickets; they won't work.
The tram  carries people to the most visited places. It starts from the railway station, goes along the main street, turns at the Grand Church a bit, goes to the Old Forest, the Zoo, Theme Park and Public Bath, then around to meet the Universities, then back. A cheap way to see most of the city is to get a ticket at the train station, get on, and enjoy the trip until you're back where you started.
Bus  lines are fair. You may expect to be able to reach nearby places fast.
There are many nice streets around, however there are many less attractive ones as well. Test your luck.
Try Nagyerdő (the Big Forest): it is beautiful.
Despite being the second largest city in the country, Debrecen has very few attractions to show for it. The Nagytemplom is a must see and easily accessible. As for museums, the Déri Museum is definitely worth a trip, but all the others really depend on how much Hungarian art interests you. Most of the major attractions are in the city park, or Nagyerdő, where you could easily spend a pleasant afternoon.
Places of Worship
Nagyerdő - The City Park
Located just north of the downtown is the 2280 hectare city park which offers fine walks as well as several opportunities for fun and entertainment.
Exchanging money can be cheaper here than in Budapest.
Avoid everything in Kálvin tér (the square on the right of the Big Church, in the middle of the circle of houses), like Gara cukrászda or Gilbert Pizzéria. They emphasize style over flavour.
Near the big church is where you can find nice cafes.
There's Csokonai restaurant, main steak house of Hungarian style, located in Kossuth street, right in front of Csokonai Szinház (opera house).
Try Flaska restaurant by the Apollo movie theater in the heart of the city. They have nice Hungarian dishes. For desert, head to the Mandula cukrászda (one of the best bakery in town) near Ember Pál street.
Calico Jack Pub and Palma Sorozo are two of the best restaurants in the town. Very popular with people visiting the town on business. The latest restaurant, Cafe Melange located on Egetem Sugarut is a very fine restaurant with amazing decor.
There are three Indian restaraunts. Kashmir, the only Indian restaurant in Debrecen open in the evening is not too bad, if you've never had Indian food before. For those who have, do not have high expectations, and be prepared to be paying over the odds for food which all seems to taste the same.
Another is Govinda, which is a pure Vegetarian restaurant. However, it is only open for lunch.
Nyíregyháza, a smaller city with several parks and squares and the water resort of Sóstó.