Thank you for your answers !
If I understand well, the best way from St Pancras is taking the bus or the tube. I hope I wouldn't get problems with the transports. I arrive at St Pancras at 8 AM. If I don't get lost, It would be possible to arrive at Thorpe's Openning, isn't it ? And about the train tickets, is it better to buy them in advance with buy internet ?
How does the reserve'nride work ? I've looked on their website but I don't understand which device I have to use ? Do I have to buy some special tickets or something ? Last time I went to thorpe, that was in the very end of june ( 26th ). I'm an engineer student, I don't really fear school trips. Moreover, I will spend two days in the park, I will be peaceful I think.
I hope I will have two good days I'm very excited about this trip