For questions about a written collection of Welsh myths compiled in the 13th Century from earlier oral tales, occasionally called the Mabinogi.
The Mabinogion is a series of tales centered on four major "branches"; it also includes other short stories.
You can read a translation on SacredTexts.com, or at Mabinogi.net. The first translation includes eight additional stories1, but the second translation is more accurate. A third translation (along with other welsh and celtic texts) is available at AncientTexts.org
1 The the-native-tales stories, which are sometimes considered supplemental to the four main stories