Gallipoli (Turkish: Gelibolu) is a peninsula locality in north-western Turkey, close to Istanbul. The Gallipoli Peninsula is the site of extensive First World War battlefields & memorials on the north bank of the Dardanelles Strait. It is a commemorative site for the Allied (British Empire, France) & Turkish forces who fought, died & were wounded there. The Gallipoli Campaign also known as the Battle of the Dardanelles was very costly for both sides & casualties & losses amount to 220,000 with a 59% casualty rate for the Allied forces & 253 000 with a 60% casualty rate for the Turkish forces.
The battle resonated profoundly among some nations involved. In Turkey, the battle is perceived as a defining moment in the history of the Turkish people - a final surge in the defence of the motherland as the centuries-old Ottoman Empire was crumbling; and in Australia & New Zealand, the then perceived duty to serve their "Mother Country" Britain, resulted in their military defeat, but their sacrifice & heroism marked the birth of a separate national consciousness in both of these countries.
The Gallipoli peninsula is one of the most sacred sites for the Turkish nation, with many monuments such as the Monument of Martyrs erected in the honor of the Turkish soldiers who died in the Battle of the Dardanelles against the Allied forces, whose defeat staved off a potential invasion of Turkey. The victory over the Allies is celebrated on 18 March as Canakkale Zaferi (Canakkale Victory), every year, with tens of thousands of Turks attending the events on the battlefields & memorials.
The area around Anzac Cove is particularly significant for Australians & New Zealanders, whose armies received their baptism in fire on the cliffs there & carved a fine military reputation under extreme adversity & enourmous loss of life; & this military disaster marked the beginning of a separate Australian & New Zealand nationhood. The 1915 landings & battles are commemorated by Australians & New Zealanders on ANZAC Day, 25 April, every year. At this time especially, Gallipoli becomes a place of pilgrimage for many Aussies & Kiwis who want to honour the memory of their forbears.
There are three main battlefield areas - Cape Helles (Turkish: Seddulbahir), Anzac / Pine Ridge & Suvla Bay (which has fewer places to visit). Depending on how detailed your itinerary is, it would be possible to visit the main sites of interest, particularly around Cape Helles & Anzac - Pine Ridge, in a single day. More realistically, two or three days allows plenty of time for an extensive tour, taking in all the battlefield sites, cemeteries & memorials. Must sees include: The Cannakale Martyrs Memorial (near Cape Helles); The British Memorial at Cape Helles; Anzac Cove; Pine Ridge Australian Memorial; New Zealand Monument, Chunuk Bair; Ataturk Statue, Chunuk Bair.
Aside from the 1915 battlefields, why not visit the new Gelibolu Milli Park visitors centre where there are excellent displays relating to the natural history of the peninsula. You can also visit the ancient fortress of Kilitbahir south of Eceabat or take a ferry across the Straits to Asia; from Canakkale, drive to what is reputed to be the site of Ancient Troy (signposted Troia) about 30 kilometres to the south. The ruins of the legendary city - complete with (reconstructed) wooden horse - are open to the public.