Stronghold

The clostest stronghold to spawn is widely used by the 9b6t playerbase. It can be accessed using a nether portal on a branch of the X+ nether highway. The portal is currently inside a obsidian room due to constant griefs destroying the rest of the stronghold and island above.

Other Strongholds
There are approximately 10 other strongholds spread out around the greater spawn region. These can easily be found by imputing the world seed into a stronghold finder. These have been used in the past as stashes for the donkey/end portal dupe. Most, however, are still widely ungriefed and unexplored.