I live in Oxford, UK, which is a lovely place, but I do wish it was a bit closer to the sea. What's the best way to get to a beach, starting from here? I sometimes have access to a car, so driving routes are interesting, but mostly I'm looking at public transport for a day trip, or single overnight stay.
Take the Oxford tube to victoria station. You can get to Several beaches from victoria. For example
Brighton is a Shingle beach Trains run direct from Victoria to Brighton
Margate is a sandy Beach Trains run direct from victoria to margate
The BBC have a page listing good beaches from around the UK and how to get to them
I may be biased because I grew up there, but I'm a big fan of the beaches around Christchurch, Bournemouth and Poole. There is 7 miles of continuous sand from Sandbanks (Poole), past Bournemouth and on to Hengistbury Head (Christchurch). From Sandbanks, head across the mouth of Poole Harbour on the chain ferry, then you've another 5 miles of sandy beach along Studland Bay.
Cross Country Trains run one direct train per hour from Oxford to Bournemouth, and the journey takes just under 2 hours. (Currently it's the xx:16 train). You can also get there by changing at Reading and Baisingstoke, which sometimes makes sense if you've just missed the direct train!
If you're aiming for the beaches at Bournemouth, it's a 10-15 minute walk from the station to the nearest patch of sand (Holdenhurst Road / Meyrick Road / down the steps). For the Pier and the Gardens, there are plenty of buses from the station.
For Sandbanks and Studland, change at Bournemouth for a train to Poole (it's normally a few minutes behind on the same platform), then walk through the shopping centre to the bus station. Sit on the top deck if you can, and enjoy some stunning harbour views as you head to the beach!
Otherwise, in a car head down the A34, then M3, M27, and get out a book. On a nice evening, especially a Friday night, you then have a 20 mile carpark across the New Forest... When you finally make it along the A31, take the Spur Road to Bournemouth or carry on for Poole. On a good day it's about 90 minutes without stopping, on a bad day 4 hours is not unheard of!
Getting to Hayling Island is fairly straightforward, a 1h 40m drive. dayoutwiththekids.co.uk has some other suggestions. Finding public transport links shouldn't be too difficult.