ADHIKR

(Al-Kahf) 18 : 97
فَمَا اسْطَاعُوا أَنْ يَظْهَرُوهُ وَمَا اسْتَطَاعُوا لَهُ نَقْبًا

So they were unable to pass over it, nor were they able to penetrate underneath.