A trip on a boat

Hi Kate;
That sounds very well great. Last month we went on a boat trip with my University colleagues,and it´s was marvelous, even the weather was very nice(beautiful, terrific, fabulous...very nice is too simple and dull).
I'll recommend  that you to do it, but you will have to be careful with the weather, iIf the weather is not good you canmight spend a horrible(unpleasant) day because, you have to take into account, the boat doesn´t have anywhere  that you can settlehide if it´s raining.
You can take the boat at 8:00 am or at 10:00 am daily, you can do it every day per week, even on Saturday's and Sunday's. The boat stopsped for thirty minutes in Bourne Castle. I'll recommend that you don´t waste(avoid wasting) your time buying a lot of suveniers  souvenirs in the shops when you first enter the castle that there are in the enter because tThe Castle is (very) big (huge) and if you spend a lot of time in the shops, you are not going to have much time to visit it. <em>(look around, explore, really see the sights, really see the castle)</em>
You can have lunch in the restaurants in the Ccastle, because you have some restaurants inside, but it is better(nicer) if you take a picnic. You will be able to eat at it in the second stop of the trip.
In the afternoon we went to a lake; there you can take advantage to do any  of the excellent water sports that are available.  We didn´t do anything, but if you are in fit, you should (at least ) try to do itsomething.
Finally, if you there are more than 15 people you have there are several discounts available, depending on the stops that you want to do.
I hope you enjoy it.
Best Regards.

Your text is perfectly understandable and correct for the most part.  However, if you want to sound more native English, this is one way to improve the article. 

Try to avoid 'very nice or very good' and substitute great, fabulous, terrific, awesome(N. America), fantastic, super etc.  In the act of recommending something you can use the present(I recommend that you...) or future tense(I will recommend that you...), both are fine.  Perhaps, if you are recommending multiple things, the future tense or even conditional(I would recommend that you do...).  Confusing?  Some is just style.

Hope that this helps.  I wish that I could write like you in the language that I am learning(French).  SC

Trip on boat

Hi Kate;
That sounds very well nice. Last month we went on a boat trip with my University collages colleagues, it´s It was marvelous, even the weather was very nice.
I recommend you to do it, but you have to be careful with about the weather, because if the weather is not good you can spend have a horrible day because, you have to take into account (this is grammatically correct but sounds a little weird here), the boat doesn´t have anywhere where you can settle(again, this is grammatically correct but not something a native speaker would say, something like "hide" or "take cover" would be better) if it ´s raining ("if it's raining" is OK, but a native speaker would probably say "if it rains").
You can take the boat at 8:00 am or at 10:00 am, and you can do it every day per of the week, even Saturday and Sunday. The boat stopped thirty minutes in Bourne Castle, I recommend you don´t waste your time buying a lot of suveniers in the shops inside that there are in the enter because the Castle is very big and if you spend a lot of time in the shops, you are not going ("you are not going" is OK, but "you won't" would be better here) to have time to visit it.
You can have lunch in the Castle, because you have there are some restaurants inside, but it is better if you take a picnic, you will be able to eat have it in the at the second stop of the trip.
In the afternoon we went to a lake, you can take advantage to do any kind of water sports , we didn´t do anything, but you are in fit, you should try to do it.
Finally, if you are more than 15 people you have there are several discounts, depending on the stops you want to do.
I hope you enjoy it.
Best Regards.

Good job!  I know there's a lot of red but really it's wasn't that bad :)