The tunnel, which measured more than 6 feet high and nearly 3 feet wide and snaked 33 feet long, was near York University and the Rexall Centre, the venue for the 2015 Pan American Games
in Toronto in July.
The tunnel was 10 feet underground, with a ladder leading down to a chamber where it was possible for a person to move around.
A conservation officer stumbled on the tunnel in January, but police told the public about it last week. The announcement came amid heightened concerns about terrorism in Canada.
Toronto Police Constable Victor Kwong told CNN on Monday that two men who dug the tunnel made it for "personal reasons" that were not criminal. CNN asked for more details such as the identities of the men and an explanation of those personal reasons. Kwong declined to provide any further information.
Some took to Twitter with the hashtag #personalreasons to mock the police.
One tweet read: "Police: 'Why'd you build a fortified, three-storey-tall sniper's nest?' Guy in camo facepaint: 'Personal reasons.' Police: 'Cool.'"
Another person posted, "Today, armed only with a beach shovel and rosary beads, I start construction on a new subway line for personal reasons. #torontotunnel"
The zingers kept coming, with "When I build my own tunnel for 'personal reasons', I'll at least have the decency to install a wine fridge."
Digging a hole is not a crime
Last week, police publicized the existence of the tunnel hoping that someone from the public would help them find out who made it.
Kwong said that tactic worked, and people who saw news reports phoned police with the names of the men, who were questioned but not arrested.
"There is no criminal offense for digging a hole," Deputy Chief Mark Saunders said last week.
Authorities have filled in the hole.
In the tunnel, plywood walls were reinforced with wooden supports.
A rosary with a Remembrance Day poppy hung from a nail on the wall. Remembrance Day honors Canadian service members who died in combat.
Last week, during a press conference, a reporter asked Saunders, "What does that tell you?"
"That tells me that this was nailed inside the tunnel on the wall," Saunders deadpanned.
The room erupted with laughter.
A tunnel in a country facing terror threats
"I wasn't overly concerned that 'Oh my goodness this is going to be something horrific,'" said the chief, a 31-year veteran of the force.
"We've got steps and measures in place" to deal with these kinds of threats, he said. "If someone is going to be nefarious in this type of way, we'll be on top of it."
In October, a soldier was shot and killed as he stood guard at Canada's National War Memorial
in Ottawa. Officials said the gunman had connections to jihadists who shared a radical Islamist ideology.
Two days before the Ottawa attack, another Canadian soldier in Quebec was run over and killed by a man whom the Royal Canadian Mounted Police described as "radicalized."
Saunders said the tunnel was found about 82 feet west of a fence that separated a densely wooded area from tennis courts at Rexall Centre, a tennis and entertainment complex on the grounds of York University.
The tunnel was equipped with electricity supplied by a generator, a sump pump to remove water, and a pulley system to remove dirt, Saunders said. It likely took more than one person to dig it out by hand. Ice that formed at the end of a hose attached to the sump pump indicates that the tunnel may have been used this winter.
"This was built with a considerable amount of sophistication," Saunders said. "The individuals responsible for building it clearly had some expertise in structural integrity."
Police also found a gas can, food and beverage containers, work gloves, a wheelbarrow and moisture-resistant light bulbs in the tunnel. Dirt covered a wooden lid that concealed the tunnel's surface entrance.
The Pan American Games involves nearly 7,000 athletes from Latin America, South America, the Caribbean and North America. It is the third-largest international sports competition after the Olympic Summer Games and the Asian Games.