River decision against a donk.

[Insistent_]

This is from a Swedish poker site. Eqiuivalent to $1/2 game.
Opposition is very bad and fishy, especially the one I'm playing against. It may have been a stupid bet on the turn (?) but everyone was autochecking, so I thought I'd take a stab at it. On the river I valuebet but get raised. They LOVE slowplaying on this site but still feels like a bet coming from nowhere??

7.50/15.00 Texas Hold'em (No Limit ) - den 20 juli 2007 19:42:06
Frida Turbo 4 (Vanlig /Cash Game )
Plats 1: lirapoker (1891.85)
Plats 2: ellerhur (602.52)
Plats 3: sergio t (3034.15)
Plats 4: tiiilt (1816.16)
Plats 5: Only (3932.49)
ellerhur SB 7.50
sergio t BB 15.00

lirapoker [9s, 7s]
ellerhur [N/A, N/A]
sergio t [N/A, N/A]
tiiilt [N/A, N/A]
Only [N/A, N/A]

tiiilt Call 15.00
Only Call 15.00
lirapoker Call 15.00
ellerhur Call 15.00
sergio t Check
*** Flop(Board): *** : [6h, Dd, Dc]
*** Bet Runda 2 ***
ellerhur Check
sergio t Check
tiiilt Check
Only Check
lirapoker Check
*** Turn(Board): *** : [6h, Dd, Dc, 8h]
*** Bet Runda 3 ***
ellerhur Check
sergio t Check
tiiilt Check
Only Check
lirapoker Bet 56.00
ellerhur Fold
sergio t Fold
tiiilt Call 56.00
Only Fold
*** River(Board): *** : [6h, Dd, Dc, 8h, 10c]
*** Bet Runda 4 ***
tiiilt Check
lirapoker Bet 156.00
tiiilt Raise to 672.00
lirapoker ??

Please explain your thought process. =)

[Spy Dog]

I usually just stare when I see Double Ds flopping like this.