Possible Clues:

• Plain sailing primarily with Bolt closing on back-to-back records
• Dry grassy plain of central Europe
• Vast Eurasian expanse
• Plain kind of aerobics exercise class
• You'd need more than seven-league boots for such a pace, by the sound of it
• Ukrainian geographical feature
• Sounds like the biggest pace in the world
• Rung to be heard, it's plain
• You'd need more than seven-league boots for a stride like that
• Wide enough to get you up a bit in Russia, by the sound of it