Some 10,000 bicyclists will swarm the streets this weekend, as they take on the 203-mile Group Health Seattle to Portland Bicycle Classic.

About one-fourth of the cyclists will complete the ride in one day, with the rest taking two days.

Riders will start Saturday at the University of Washington’s Montlake parking lot and finish Sunday in northeast Portland at Holladay Park. They will travel through Kent, Centralia, Chehalis, Winlock, Toledo, Castle Rock and Kelso on their way to Portland.

The Group Health STP is organized by Cascade Bicycle Club. Registration fees of $110 for members and $120 for nonmembers help fund the organization’s education, advocacy and rides program.

Unlimited Digital Access. $1 for 4 weeks.

The 35th annual event attracts a range of riders. This year, the oldest is 88 years old.

“The energy of 10,000 riders starting in Seattle and arriving in Portland and camping together along the way is a thrilling experience,” said Executive Director Elizabeth Kiker.

Communications Director Anne-Marije Rook said this year tickets sold out at a record pace — within two weeks of registration.

Last year participants came from 45 states and six countries. Nearly 8,200 riders were from Washington and about 1,200 were from Oregon.

“Every person rides for a specific reason whether it’s a bucket list, age milestone or in memory of someone who has passed,” Rook said.