It's wonderful to hear that you will be over in July for the racing festival in Killarney!
There are a couple of options, fly and drive or come in your own car by ferry. We have a getting to Ireland
page that is handy to find flight and ferry providers so you can check out the options and costs directly. Cork airport would be the closest when here but there is also Dublin from Bristol too. Hire cars
would be available from both locations. Public transport is also an option from Cork airport to Killarney, Transport for Ireland
has a journey planner that will give details of the providers if this is something you are interested in.
With ferries, there are two choices to Rosslare, from Pembroke or Fishguard. Again, use the ferries search page for the different providers for times and costs. The drive down the coast towards Cork and across to Killarney is a lovely one taking about 4 hours.
Hopefully, this will give you some ideas to get you started.
Is this your first time at the Killarney Racing Festival?