Kórnik is accessible forst of all by buses, the transport company of the Commune of Kórnik (Kombus) serves several bus lines from Poznan – the best solution is to take line #501 from bus station Rondo Rataje, where yoo can get from the centre using trams : #3, #4, #6, #11, #12, #13. Line #501 run appr. twice an hour in peak hours, and once an hour in between-peak period. Another solution are lines : #502 (peak hours only), or 560 and 561 heading to the town of Zaniemysl. More timetables and fares : 
Another option is to use PKS buses – at least 40 daily leave from the coach station. Timetable : 
If you really like trains you can use one going from Poznań to Kórnik – there are many of them, but the station in Kórnik is situated 3 kms from the centre (however – you can use Kórnik local buses to get from the station to the centre : #502, #590, #591, #592, #594.
Getting to Kórnik by car is also easy : using express road number 11 the journey shouldn’t take more than 20-25 min. Parking place : on the main square (a cheaper option) or nearby the Castle, next to the snack-bars anr souvenir stands (definitely more expensive, but closer).
Kórnik and its closest vicinities are also served by Kombus buses, but for most of tourists they’re useless, as both main Kórnik attractions (the Castle and parish church) are located appr. 200m from each other. However, buses can be useful for those planning to spend some time on one of the surrounding lakes.
The Dzialynski Castle – a castle with its roots in deep Middle Ages, the present shape is the result of the XIXth cent. reconstruction. During the visit in the castle you will see beautiful interiors with original furniture from (mostly) XVIIIth and XIXth cent, wonderful floors made of roots of trees, some paintings, musical instruments, souvenirs brought from all-over-the world by one of the Castle’s owners and – last but not least – the portrait of Mrs. Teofila – better known as Kórnik White Lady – a good ghost of the castle appearing every midnight in the park nearby. On the second floor there’s a unique armory collection and some book from extra precious Kórnik Library (which is a part of the Polish Academy of Sciences) : the manuscript of the first edition of Nicolas Copernicus’s Works, the first guide-book about Poznań, the first printed Bible in Polish (II half of XVIth cent) and many other books or manuscripts.
The Dendrological Park – one of the biggest in Poland with more than 3 500 tree species from the north semisphere, mostly from Japan, China and America
the parish church from XVth cent. with a neogothic fasade and tombs of the Gorka Family (the previous Castle owners)
From Kórnik you can go back to Poznan with a stop in Rogalin (where you can visit a classicistic palace of the Raczynski Family and Poland’s oldest oak trees), to Zaniemysl with marvellous lakes, to Zerkow-Czeszewo Landscape Park (covering the natural Warta river, or simply further suoth-east to Gołuchów or Kalisz – Greater Poland’s second biggest city.
Just next to Kórnik, in Bnin (2 kms) you can see the birthplace of Wisława Szymborska (a Literature Nobel Prize Winner in 1990s) and some nice XIX-century tenement houses and a Town Hall.
An interesting thing for nature-lovers can be a beaver’s trail starting in a village Czmoniec, leading alondside Warta river, where beavers’ habits are presented on 9 boards and – with some luck – you can watch these nice rodents.