Only... One or two? There's definitely one that tunnels under it.
Hlaalu's stronghold wasn't bad, just a few dozen jumps* south of Balmora itself, as long as you start on the right side of the river (or up a cliff from Hla Oad). Telvanni's was pretty out of the way, being in the start of the mountains west of Tel Fyr... And I can't remember where Redoran's was. Somewhere by Ald-Ruhn?
Although, to be fair, I too just used one of the unoccupied houses in Balmora because it was shorter to the Silt Strider.
*(i.e. "a short run" )