Here is a list of 8 popular beaches within a reasonable drive of Cork City.

These are arranged in order of distance from Cork City.
Be aware that on busy days the journey time could be greatly increased.
Beach life in Ireland works like this.
In Summer and in good weather they will be very packed with daytrippers so expect traffic delays which increases in direct proportion the amount of sunshine.
The busiest days are Sundays, Bank Holiday Mondays and Saturdays when the weather is good.   When not so good, you may easily have the whole beach to yourself.   Least busy days are any week days.
Essentially those with a Blue Flag mean that the Water Quality is of an acceptable European standard.   Unfortunately Blue Flag does not cover other aspects of the environment such as litter, toilets and animal waste.
Under no circumstances should you swim at a beach that you are unfamiliar with.   Most beaches have Life Guards during the Summer.   If there are no life guards about ask a local about the safety aspect of the area .  If you cannot find anyone to ask - Do not swim.   There are swim related fatalities every summer in this country.
Be prepared –  beaches can be very windy regardless of the sunshine!
If you intend to stay for the day, try and arrange to bring a picnic.   Most of the beaches do not have take away food facilities nearby.
The star rating given to each of the beaches below is based on the ‘overall experience’ not just on specific elements. The higher the number of stars the better.
Of course there are other beaches in the area, but those below are favorites.  Any additional comments on Irish Beach experiences are most welcome. 

Beach: Myrtleville and Fountainstown

Km / Miles from Cork City: 22k / 14m (Drive time – 30 minutes)
Direction: SOUTH-Take the N28 via Carrigaline
Nearest town: Carrigaline 4k / 2.5m

Public Transport: 220A bus. Myrtleville Beach is 10 minutes walk down the hill from Crosshaven Rugby Club. The bus stops in Fountainstown

Food/Snacks: Small Shop near Beach. Pub/Restaurant near beach .
Comment: Myrtleville is a small sandy beach mainly used by residents of nearby holiday homes. Limited parking on the road.  You can walk or drive from here to Fountainstown beach – about 1k away.  Fountainstown beach is stony with lots of seaweed.  It has a large free car park.
Overall star Rating: Fountainstown 2** Myrtleville 3***
Toilet Facilities: No at Myrtleville, Yes at Fountainstown – just about adequate
Other options:   If time allows pay a visit to the nearby sailing town of Crosshaven (location of the oldest sailing club in the world – RCYC)

Beach: Garrettstown

Km / Miles from Cork City: 34k / 21m   ( Drive Time – 40 minutes)
Direction: EAST – Take the N27 via Cork Airport, Riverstick, Belgooly, Kinsale, Ballinspittle.
Nearest town: Ballinspittle 2k / 1.25m

Public Transport: 226 bus (Summer only. Not all services)

Food/Snacks: Small Shop and Tea Room
Comment: Large sand and stony Blue Flag beach, great for surfing. Lifeguards present in Summer Season.  Lots of parking on the beach front. Ask for directions to the nearby cliff walk, which affords fantastic views of the Celtic Sea on a clear day. 
Overall star Rating: 4 ****
Toilet Facilities:   Adequate
Other Options: Walk around Kinsale town – very picturesque. Visit Ballinspittle and find the ‘moving statue’ !!!

Beach: Garryvoe

Km / Miles from Cork City: 34 k / 21m (Drive Time – 40 Minutes)
Direction: EAST – Take the N25 via Midleton, Castlemartyr, Ladysbridge.
Nearest town: Ladysbridge 2k / 1.25m 
Public Transport: 240 bus (Not all services)

Food/Snacks: Small Shop near beach, Garryvoe Hotel near beach serving full meals and bar food.
Comment: A very large sand and stony Blue Flag Beach. Life guards present in Summer Season.  Gets extremely busy on fine weekends.  Lots of parking along the beach front.  Good childrens playground on beach front.  Fast food vans are there on fine weekends.
Overall star Rating: 3 ***
Toilet Facilities: Just about adequate
Other Options: Drive to the delightful fishing village of Ballycotton and ask for directions to the cliff walk where excellent view of the ocean can be seen.  Visit the Stephen Pearse Pottery shop on the road to Ballycotton.

Beach: Youghal  (Pronounced: YAWL)

Km / Miles from Cork City: 48k / 26m (Drive time – 50 Minutes)
Direction: EAST – Take N25 via Midleton, Castlemartyr, Killeagh
Nearest town: Youghal – 300 metres

Public Transport: 40 bus & 260 bus
Food/Snacks: Lots of food options in Youghal town
Comment: An extremely long and popular Blue Flag Beach.  Was one of the main beach areas for Cork City residents in the 50’s and 60’s when a train ran from the city right to the beach.  Lots of parking on the main road.
Overall star Rating: 3 ***
Toiliet Facilities: Just about adequate
Other Options:   Drive a further 10k east to the lovely village of Ardmore (in County Waterford) where there is also a super beach.

Beach: Courtmacsherry

Km / Miles from Cork City: 50k / 31miles   (Drive time – 50 minutes)
Direction: WEST – Take N71 via Half Way, Bandon, Timoleague
Nearest town: Courtmacsherry – 500 metres .

Public Transport: 239 bus  (Not all services)

Food/Snacks: Shops and pubs in Courtmacsherry village.  Fast food vans in Summer time.
Comment:   Medium sized sandy beach.  Very tidal due to it’s snug location deep in Courtmacsherry bay.  Sailing and surfing lessons available on the beach.  Adequate parking along the beach front.  Mainly used by residents of nearby holiday homes.
Overall star Rating:   4 ****
Toilet Facilities: Not Known
Other Options: Stroll around the lovely village and also nearby Timoleague.  Do the 7 heads walk which begins near Courtmacsherry beach.  Local shops sell a guide book explaining aspects of this lovely walk. Ask locals for details. 

(Additional note: Although Coutmacsherry is fantastic for walking and interesting harbour the beach is NOT for swimming due to VERY strong currents and some issues about water quality - there is a large algae bloom up the estuary in July/August - if you want swimming try Blind Strand or Dunworly nearby - but these have no lifeguards. Courtmacsherry has fine toilets - in the pubs shich don't mind you using them.)

Beach : Inchydoney (Pronounced: INCH-A-DONNY)

Km / Miles from Cork City: 50k / 31miles (Drive time – 55 minutes)
Direction: SOUTH – Take N71 via Bandon, Clonakilty
Nearest town: Clonakilty 4k / 2.5miles

Public Transport: None
Food/Snacks: Small kiosk near beach with very erratic opening times. Lodge and Spa hotel nearby where full meals (expensive) and bar food is available.
Comment: Very large sandy Blue Flag Beach.  Lifeguards on duty during Summer Season.
Overall star Rating: 4 ****
Toilet Facilities: Old and Just Adequate
Other Options: Stroll around Clonakilty town, a pretty place. Visit the Model Railway village, a very popular attraction. Dunmore house hotel, 3 miles from Clonakilty, difficult to find but great bar food and wonderful views. 

(Additional note: If you don't like the old toilets go into the Dunes pub in the Inchydoney hotel - just to the left of the main entrance - this is also a great pub for after swim drinks or food, especially afternoon tea - and is remarkable value compared to the prices in the hotel resteraunt. If wind is from the west go to the beach beyond the hotel to the east - stairs down in front of the appartments - this is more sheltered from west winds)

Beach: The Warren

Km / Miles from Cork City: 58k / 36 miles (Drive time – 1 hour 15 mins)
Direction: WEST – Take N71 via Bandon, Clonakilty, Rosscarbery
Nearest town: Rosscarbery 2k / 1.25miles

Public Transport: 237 bus. 20 minutes walk from Rosscarbery.

Food/Snacks: Small shop at beach with very erratic opening times serving Tea and Coffee. Shops and Pubs in Rosscarbery and also hotel called Celtic Ross nearby on main road is good.
Comment: Nearby is a pier suitable for fishing from.  Safe for swimming.  Lifeguards on site in summer months.  You can walk using a safe path over the headland on the left into nearby Owenahincha beach. Small pitch and putt course beside the beach where clubs and balls can be hired.  It's 6 euro per 18 hole round.
Overall star Rating: 4 ****
Toilet Facilities: Just about adequate
Other Options :  Visit the nearby pretty towns of Glandore, Union Hall and Rosscarbery.  Boating available on the lake below Rosscarbery town. Take the path over the headland to nearby Owenahincha. Good pitch and putt courses behind the beach. 

Beach: Owenahincha (very near the Warren) (Pronounced: OH-NA-HIN-CHA)

Km / Miles from Cork City: 58k / 36miles (Drive time 1hour 15 mins)
Direction: WEST – Take N71 via Bandon, Clonakilty, Castlefreke
:   Very nice sandy beach but the area is somewhat spoiled by derelict buildings and some badly laid out mobile home parks

Public Transport: None

Overall star Rating: 2 ** Do not swim here as strong currents and  swim fatalities in past !
Toilet Facilities: Old and just adeqate
Other Options:   Take the path over the headland to the Warren Beach.  Visit the old castle at Castlefreke.